Cookies on Invasive Species Compendium

Like most websites we use cookies. This is to ensure that we give you the best experience possible.

 

Continuing to use www.cabi.org  means you agree to our use of cookies. If you would like to, you can learn more about the cookies we use.

Have you tried our Horizon Scanning Tool (beta) for prioritizing invasive species threats?

We’d value your feedback on the tool. Our survey takes only five minutes to complete.

Datasheet

Rana catesbeiana (American bullfrog)

Summary

  • Last modified
  • 14 July 2018
  • Datasheet Type(s)
  • Invasive Species
  • Natural Enemy
  • Preferred Scientific Name
  • Rana catesbeiana
  • Preferred Common Name
  • American bullfrog
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Chordata
  •       Subphylum: Vertebrata
  •         Class: Amphibia
  • Summary of Invasiveness
  • The American bullfrog has been transported around the world primarily with the intention of cheaply cultivating its large and meaty hind legs for human consumption. It is also of commercial interest to biological supp...

Don't need the entire report?

Generate a print friendly version containing only the sections you need.

Generate report

Pictures

Top of page
PictureTitleCaptionCopyright
Adult American bullfrog, (Rana catesbeiana). Chodikee Lake, Ulster County, New York, USA
TitleAdult
CaptionAdult American bullfrog, (Rana catesbeiana). Chodikee Lake, Ulster County, New York, USA
Copyright©Russ Ottens/University of Georgia, Bugwood.org/Creative Commons Attribution 3.0 License. CC BY 3.0 US
Adult American bullfrog, (Rana catesbeiana). Chodikee Lake, Ulster County, New York, USA
AdultAdult American bullfrog, (Rana catesbeiana). Chodikee Lake, Ulster County, New York, USA©Russ Ottens/University of Georgia, Bugwood.org/Creative Commons Attribution 3.0 License. CC BY 3.0 US
Chytridiomycosis; swabbing a North American bullfrog, farmed for the food trade in China, to test for Batrachochytrium dendrobatidis infection.
TitleSwabbing
CaptionChytridiomycosis; swabbing a North American bullfrog, farmed for the food trade in China, to test for Batrachochytrium dendrobatidis infection.
Copyright©Lisa M. Schloegel
Chytridiomycosis; swabbing a North American bullfrog, farmed for the food trade in China, to test for Batrachochytrium dendrobatidis infection.
SwabbingChytridiomycosis; swabbing a North American bullfrog, farmed for the food trade in China, to test for Batrachochytrium dendrobatidis infection.©Lisa M. Schloegel
Chytridiomycosis; swabbing the hindfoot webbing of a North American bullfrog. to test for infection by the fungus Batrachochytrium dendrobatidis.
TitleSwabbing
CaptionChytridiomycosis; swabbing the hindfoot webbing of a North American bullfrog. to test for infection by the fungus Batrachochytrium dendrobatidis.
Copyright©Lisa M. Schloegel
Chytridiomycosis; swabbing the hindfoot webbing of a North American bullfrog. to test for infection by the fungus Batrachochytrium dendrobatidis.
SwabbingChytridiomycosis; swabbing the hindfoot webbing of a North American bullfrog. to test for infection by the fungus Batrachochytrium dendrobatidis.©Lisa M. Schloegel
Chytridiomycosis; North American bullfrogs in Taiwan, farmed for the international food trade.
TitleNorth American bullfrogs in culture
CaptionChytridiomycosis; North American bullfrogs in Taiwan, farmed for the international food trade.
Copyright©Lisa M. Schloegel
Chytridiomycosis; North American bullfrogs in Taiwan, farmed for the international food trade.
North American bullfrogs in cultureChytridiomycosis; North American bullfrogs in Taiwan, farmed for the international food trade.©Lisa M. Schloegel
Chytridiomycosis; North American bullfrogs in Taiwan, farmed for the international food trade.
TitleNorth American bullfrogs in culture
CaptionChytridiomycosis; North American bullfrogs in Taiwan, farmed for the international food trade.
Copyright©Lisa M. Schloegel
Chytridiomycosis; North American bullfrogs in Taiwan, farmed for the international food trade.
North American bullfrogs in cultureChytridiomycosis; North American bullfrogs in Taiwan, farmed for the international food trade.©Lisa M. Schloegel
Chytridiomycosis; close view of north American bullfrogs in Taiwan, farmed for the international food trade.
TitleNorth American bullfrogs in culture
CaptionChytridiomycosis; close view of north American bullfrogs in Taiwan, farmed for the international food trade.
Copyright©Lisa M. Schloegel
Chytridiomycosis; close view of north American bullfrogs in Taiwan, farmed for the international food trade.
North American bullfrogs in cultureChytridiomycosis; close view of north American bullfrogs in Taiwan, farmed for the international food trade.©Lisa M. Schloegel

Identity

Top of page

Preferred Scientific Name

  • Rana catesbeiana Shaw, 1802

Preferred Common Name

  • American bullfrog

Other Scientific Names

  • Lithobates (Aquarana) catesbeianus Dubois, 2006
  • Lithobates catesbeianus Dubois, 2006
  • Rana (Aquarana) catesbeiana Dubois, 1992
  • Rana (Aquarana) catesbeiana Hillis, 2007
  • Rana (Lithobates) catesbeiana Shaw, 1802
  • Rana (Novirana) catesbeiana Hillis and Wilcox, 2005

International Common Names

  • English: bullfrog; common bullfrog; North American bullfrog
  • Spanish: rana mugidora; rana toro; rana toro Americana
  • French: grenouille d'Amérique; grenouille taureau; grenouille-taureau americaine; ouaouaron

Local Common Names

  • Brazil: rã-touro
  • Germany: ochsenfrosch
  • Italy: rana toro
  • Netherlands: grote kikker
  • Sweden: oxgroda

Summary of Invasiveness

Top of page

The American bullfrog has been transported around the world primarily with the intention of cheaply cultivating its large and meaty hind legs for human consumption. It is also of commercial interest to biological supply houses, fish bait suppliers, the pet trade, and pond landscapers. In North America in the early 20th Century it was released outside of its natural range by wildlife agencies keen on introducing a new game species (Lannoo, 1996; Tangley, 2003). Once liberated it is extraordinarily prolific, prone to migration, and highly adaptable to new environments. It grows into a relatively large, voracious, and indiscriminate predator that can come to dominate the margins of lakes and ponds. It competes with native anurans. Larvae can have a significant impact upon benthic algae, and thus perturb aquatic community structure. Adults may be responsible for significant levels of predation on native anurans and other aquatic herpetofauna, such as snakes and turtles. The species also contributes to the spread of pathogens such as the chytrid fungus, Batrachochytrium dendrobatidis (Garner et al., 2006). R. catesbeiana has been identified by the World Conservation Union (IUCN) as one of the world’s 100 worst invasive alien species (ISSG, 2005).

Taxonomic Tree

Top of page
  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Chordata
  •             Subphylum: Vertebrata
  •                 Class: Amphibia
  •                     Order: Anura
  •                         Family: Ranidae
  •                             Genus: Rana
  •                                 Species: Rana catesbeiana

Notes on Taxonomy and Nomenclature

Top of page

The American bullfrog is a member of the nearly cosmopolitan family Ranidae. For most of the past 200 years this species has been unambiguously assigned to the genus Rana and the species R. catesbeiana, Shaw, 1802. Over the past 30 years, however, advances in biochemical systematics have led to both increased knowledge and increased contention concerning how new and ever-more refined data sets should be interpreted and taxonomically expressed. Thus, there are today numerous taxonomic synonyms for R. catesbeiana, e.g. Lithobates catesbeianus,Aquarana catesbeiana, and Novirana catesbeiana, that have received varying degrees of acceptance amongst herpetological systematists and the broader zoological community (Frost 2009).

An illustration of this is found in the Atlas of Amphibians of China by Fei, L. et al (1999), wherein the “Bull Frog” is identified taxonomically as Rana (Aquarana) catesbeiana Hillis 2007. In a paper by Frost et al (2006), it is proposed that the American bullfrog and its closest ranid relatives be moved from the genus Rana to the genus - formerly subgenus - Lithobates. This taxonomic reassignment may last or it may not, as the results from future investigations of the family Ranidae emerge. One of the co-authors in Frost et al (2006) recommends adopting the device of employing subgenera to accommodate Frost et al, e.g. Rana (Lithobates) catesbeiana (Green 2007). Currently, and at least for the time being, it appears that Lithobates catesbeianus (Shaw, 1802) will most likely supersede Rana catesbeiana and all other proposed or resurrected taxonomic synonyms as the preferred scientific name for the American bullfrog. However, anyone searching for literature references that predate Frost et al (2006) will need to be aware that virtually the entire historical database for this species is assigned, and in many cases continues to be assigned, to Rana catesbeiana
 
Collins and Taggart (2009) in their influential list - Standard Common and Current Scientific Names for North American Amphibians, Turtles, Reptiles, and Crocodilians - have unilaterally declared ‘Lithobates catesbeianus’ to be the new scientific standard. However, Pauly et al (2009) - Taxonomic Freedom and the Role of Official Lists of Species Names - point out in a comprehensive and compelling way that ‘official’ lists of scientific names can have a confounding influence on objective taxonomic discussion, taxonomic stability, and the adoption, usage, and understanding of taxonomic names by non-taxonomists. 
 
Consistency in biological nomenclature is not strictly a taxonomist’s concern. Today legislators, policy analysts, lawyers, customs agents and wildlife regulators all have a need to know exactly what taxon they are dealing with and how to unambiguously represent and recognize that taxon in writing. In this context common names can become as important as their scientific alternatives. For example, the common name ‘American bullfrog’ is almost completely unambiguous in which species it represents. However, in Collins and Taggart (2009) the common name for this species is listed simply as ‘bullfrog’. The problem here is that in global terms there are also - among others - an ‘African bullfrog’ (Pyxicephalus adspersus), an ‘edible bullfrog’ (Pyxicephalus edulis), an ‘Indian bullfrog (Hoplobatrachus tigerinus)’, an Australian ‘bullfrog’ (Limnodynastes dorsalis), and a ‘South American bullfrog’ (Leptodactylus pentadactylus). It is therefore reasonable to recommend that either ‘American bullfrog’ or ‘North American bullfrog’ be adopted as the international standard common name, as in Lannoo (2005), and used consistently to eliminate confusion.

Description

Top of page

R. catesbeiana is not the largest frog species in the world but it is one of the top ten (and the largest true frog in North America) with a maximum body length slightly in excess of 200 mm (typical length 90-152 mm) and body weight up to 0.5 kg. Like most frogs, it undergoes a drastic metamorphosis during its life cycle, passing from a young aquatic life phase with branchial respiration, predominantly plankton feeding, iliophagous or herbivorous, to reach adult life as an animal with pulmonary and skin respiration and a carnivorous feeding habit (Teixeira et al., 2001). Bullfrog tadpoles are also very large by frog standards (80-150 mm) and can take from 12 to 48 months to reach metamorphosis. A bullfrog tadpole’s body can be as large as a golf ball with a relatively long, high-finned and muscular tail. The colouration of the tadpole stage is brown to light olive with small black spots scattered across the head and upper body. At metamorphosis the tadpoles resorb their gills and finned tails while transforming into juvenile miniatures of adult bullfrogs but without secondary sexual characters. The colour of adults varies from olive, green or brownish on the dorsum with vague spots or blotches; the head is lighter green, and the legs blotched or banded; the eardrums are conspicuous. The hind feet are fully webbed. The skin is mostly smooth. There are no dorsolateral folds; a short fold extends from the eye over and past the eardrum to the forearm.

Bullfrogs become sexually dimorphic as they mature. Males develop yellow skin pigments on the chin and throat, and the ear covering (tympanic membrane) enlarges to several times the diameter of the eye. On the other hand, as females mature they tend to retain the superficial morphology and colouration of the juvenile stage, e.g. they lack yellow pigmentation on the chin and throat and the tympanic membrane remains about the same diameter as the eye.
 
Only adult male bullfrogs produce the advertisement call. They do this by trapping air between the lungs and the vocal pouches. The trapped air is forced back and forth over the larynx which generates the sound of the male’s call (Gans, 1974). The vocal pouches are located on either side of the throat, just below the jaw hinge, and were thought until recently to be the primary source of amplification and broadcast of sound. However, Purgue (1997) has shown that more sound is emitted by the male’s enlarged tympanic membrane than by the vocal pouches. A calling male has longitudinal folds of stretched throat skin that are aligned with the bones of the lower jaw beneath the angle of the mouth. The advertisement call of male bullfrogs communicates a variety of signals. It identifies the location of adult males in reproductive condition. It also attracts other males to form a lek, or calling aggregation (Emlen, 1976), and communicates territorial rights and neighbour-stranger discrimination (Boatright-Horowitz et al., 2000; Bee and Gerhardt, 2001; Bee, 2003). 
 
The eggs of the American bullfrog are very small and appear black or dorsally black with a slightly lighter undersurface. Each egg is surrounded by a jelly capsule with additional jelly that creates a loose cohesion to the entire mass of eggs. A female bullfrog in her first year may produce a single egg mass of only a few hundred eggs, but as she increases in age her egg production increases as well.   By her third year she will be capable of producing 20-30,000 (FAO, 2005). At least in some cases, there are two separate clutches produced at consecutive spawning events in a single season. A bullfrog egg mass can be anywhere from 20 cm to over 1 metre across and sits at the surface in order to facilitate oxygen diffusion. The eggs will hatch in 3 to 5 days (Bury and Whelan, 1984).

Distribution

Top of page

R. catesbeiana is native to eastern North America, ranging naturally from Nova Scotia, southern Quebec and Ontario in Canada, down through the eastern United States and Mississippi drainage, and southward along the east coast of Mexico. It has been introduced to Hawaii, parts of the western USA and Canada, Mexico and the Caribbean, South America, Europe and Asia (ISSG, 2005). In the central United States it is difficult to say for certain where natural populations end and alien populations begin, but there is no disputing the fact that all occurrences west of the Rocky Mountains are the result of translocation and release during the late 19th century and throughout the 20th. (It is known that bullfrogs were introduced to areas of California and Colorado in the early 1900s -- University of Michigan Museum of Zoology, 2005).

 

Distribution Table

Top of page

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

ChinaPresentIntroduced1960s Invasive Fei et al., 1999; DIAS, 2004; Kraus, 2009
-HainanPresentIntroducedTeixeira et al., 2001
-Hong KongPresent, few occurrencesIntroducedSantos-Barrera et al., 2009Escaped market animals have been found but no evidence yet of established populations
-HubeiPresentIntroducedTeixeira et al., 2001
-SichuanPresentIntroduced Invasive Santos-Barrera et al., 2009Feral populations have become established
-XinjiangPresentIntroduced Invasive Santos-Barrera et al., 2009Feral populations have become established
-YunnanPresentIntroduced Invasive Santos-Barrera et al., 2009Feral populations have become established
-ZhejiangLocalisedIntroduced Invasive Wu et al., 2005; Li et al., 2006; Wang and Li, 2009Feral populations have become established on the Zhoushan archipelago and neighbouring mainland China
IndonesiaPresentIntroduced1970DIAS, 2004; FAO, 2005; Kusrini and Alford, 2006; Santos-Barrera et al., 2009
IsraelPresentIntroduced Invasive Kraus, 2009
JapanPresentIntroducedTeixeira et al., 2001
-Bonin IslandPresentIntroducedKraus, 2009
-HokkaidoPresentIntroduced Invasive Santos-Barrera et al., 2009Southern Hokkaido
-HonshuPresent1920sHirai, 2004; Kraus, 2009
-Ryukyu ArchipelagoPresentIntroducedKraus, 2009; Santos-Barrera et al., 2009
Korea, Republic ofPresentIntroduced Invasive DIAS, 2004; Kraus, 2009
LaosPresentIntroducedFAO, 2005
MalaysiaPresentIntroducedHardouin, 1997; Teixeira et al., 2001; FAO, 2005; Kraus, 2009; Santos-Barrera et al., 2009Farmed
PhilippinesPresentIntroducedHardouin, 1997; Santos-Barrera et al., 2009Farmed near Manila
SingaporePresentIntroduced Invasive Tan and Tan, 2002; Baker, 2009; Santos-Barrera et al., 2009Now common in reservoirs. Bukit Timah area & Lower Peirce Reservoir
Sri LankaPresentIntroduced Invasive Kraus, 2009
TaiwanPresentIntroduced1924 & 1951 Invasive DIAS, 2004; FAO, 2005; Hou et al., 2006; Kraus, 2009; Santos-Barrera et al., 2009Imported for aquaculture in the 1950s. Feral populations have become established and are sold in pet shops
TajikistanPresentIntroduced Invasive Kraus, 2009
ThailandPresentIntroducedTeixeira et al., 2001; DIAS, 2004; FAO, 2005; Santos-Barrera et al., 2009Began culturing bullfrogs in the early 1990s technically supported by Chulalongkom University
VietnamPresentIntroducedFAO, 2005

Africa

NamibiaPresentIntroducedKraus, 2009
Spain
-Canary IslandsPresentIntroducedKraus, 2009; Santos-Barrera et al., 2009

North America

CanadaPresentPresent based on regional distribution.
-British ColumbiaLocalisedIntroduced1930sOrchard, 1999; NatureServe, 2005; Kraus, 2009Southern Vancouver Island; Gulf Islands; Sunshine Coast; Lower Mainland; Osoyoos Lake
-New BrunswickPresentNativeMcAlpine, 1997
-Nova ScotiaPresentNativeWeller and Green, 1997
-OntarioPresentNativeISSG, 2005
-QuebecPresentNativeISSG, 2005
MexicoWidespreadNativeKellog, 1932; Smith and Taylor, 1948; FAO, 2005; CONABIO, 2008; Kraus, 2009; Santos-Barrera et al., 2009Native to east coast. Introduced populations in 15 states and the Federal District. See CONABIO (2008) for more information on introductions.
USAPresentPresent based on regional distribution.
-AlabamaPresentNativeNatureServe, 2005
-ArizonaPresentIntroducedBury and Whelan, 1984; Lannoo, 2005; NatureServe, 2005; Kraus, 2009; McKercher and Gregoire, 2009Established in San Bernadino Wildlife Refuge and Leslie Canyon National Wildlife Refuge in Cochise county; also in Buenos Aires National Wildlife Refuge in Pima county
-ArkansasPresentNativeNatureServe, 2005
-CaliforniaWidespreadIntroduced1896 - 1915 Invasive Bury and Whelan, 1984; Lannoo, 2005; University of Michigan Museum of Zoology, 2005; Kraus, 2009; McKercher and Gregoire, 2009
-ColoradoLocalisedIntroduced1913 - 1914Kraus, 2009Two Ponds National Wildlife Refuge, Jefferson County
-ConnecticutPresentNativeNatureServe, 2005
-DelawarePresentNativeNatureServe, 2005
-FloridaPresentNativeUniversity of Michigan Museum of Zoology, 2005
-GeorgiaPresentNativeNatureServe, 2005
-HawaiiLocalisedIntroduced1897 - 1899 & 1902ISSG, 2005; Lannoo, 2005; Kraus, 2009; McKercher and Gregoire, 2009; Santos-Barrera et al., 2009Oahu Forest National Wildlife refuge and James Campbell National Wildlife Refuge in Honolulu county
-IdahoPresentIntroduced1890NatureServe, 2005; Kraus, 2009
-IllinoisPresentNativeNatureServe, 2005
-IndianaPresentNativeNatureServe, 2005
-IowaPresentNativeNatureServe, 2005; Kraus, 2009; McKercher and Gregoire, 2009Introduced in the 1930s & 1960s
-KansasPresentNativeNatureServe, 2005
-KentuckyPresentNativeNatureServe, 2005
-LouisianaPresentNativeNatureServe, 2005
-MainePresentNativeNatureServe, 2005
-MarylandPresentNativeNatureServe, 2005
-MassachusettsPresentNativeNatureServe, 2005; Kraus, 2009; McKercher and Gregoire, 2009Wellfleet Bay Sanctuary; Normans Land Island National Wildlife Refuge, Middlesex county
-MichiganPresentNativeNatureServe, 2005
-MinnesotaPresentNativeNatureServe, 2005
-MississippiPresentNativeNatureServe, 2005
-MissouriPresentNativeNatureServe, 2005
-MontanaPresentIntroduced1920NatureServe, 2005; Kraus, 2009
-NebraskaLocalisedNativeNatureServe, 2005; Kraus, 2009; McKercher and Gregoire, 2009
-NevadaLocalisedIntroduced1920-1938NatureServe, 2005; Kraus, 2009; McKercher and Gregoire, 2009Pahranagat National Wildlife Refuge, Lincoln county
-New HampshirePresentNativeNatureServe, 2005
-New JerseyPresentNativeNatureServe, 2005; McKercher and Gregoire, 2009Cape May National Wildlife Refuge, Cape May county
-New MexicoPresentIntroduced1885NatureServe, 2005; Kraus, 2009
-New YorkPresentNativeNatureServe, 2005
-North CarolinaPresentNativeNatureServe, 2005
-North DakotaAbsent, formerly presentKraus, 2009
-OhioPresentNativeNatureServe, 2005
-OklahomaPresentNativeNatureServe, 2005
-OregonWidespreadIntroduced1931NatureServe, 2005; McKercher and Gregoire, 2009
-PennsylvaniaPresentNativeNatureServe, 2005
-Rhode IslandPresentNativeNatureServe, 2005
-South CarolinaPresentNativeNatureServe, 2005
-South DakotaPresentNativeNatureServe, 2005; Kraus, 2009
-TennesseePresentNativeNatureServe, 2005
-TexasPresentNativeNatureServe, 2005; Kraus, 2009
-UtahLocalisedIntroducedNatureServe, 2005; Kraus, 2009; McKercher and Gregoire, 2009Fish Springs National Wildlife Refuge, Juab county
-VermontPresentNativeNatureServe, 2005
-VirginiaPresentNativeNatureServe, 2005
-WashingtonWidespreadIntroduced1910NatureServe, 2005; Kraus, 2009; McKercher and Gregoire, 2009
-West VirginiaPresentNativeNatureServe, 2005
-WisconsinPresentNativeUniversity of Michigan Museum of Zoology, 2005
-WyomingLocalisedIntroducedNatureServe, 2005; Kraus, 2009

Central America and Caribbean

Costa RicaPresentIntroducedSantos-Barrera et al., 2009
CubaPresentIntroduced1915Teixeira et al., 2001; FAO, 2005; Kraus, 2009; Santos-Barrera et al., 2009
Dominican RepublicPresentIntroduced1955Kraus, 2009; Santos-Barrera et al., 2009
El SalvadorPresentIntroducedFAO, 2005
GuatemalaPresentIntroducedFAO, 2005
HaitiPresentIntroducedKraus, 2009
JamaicaPresentIntroduced1967 Invasive Mahon and Aiken, 1977; Kraus, 2009; Santos-Barrera et al., 2009Great Morass of the Black River
PanamaPresentFAO, 2005
Puerto RicoPresentIntroduced1935López-Flores et al., 2003; FAO, 2005; Kraus, 2009; Santos-Barrera et al., 2009Humacao Nature Reserve

South America

ArgentinaLocalisedIntroducedSanabria et al., 2011a; Sanabria et al., 2011b; Sanabria et al., 2005; Akmentins and Cardozo, 2010Present in the following provinces: Buenos Aires, Córdoba, Mendoza, Misiones, Salta, San Juan
BrazilPresentIntroduced1935 - mid 1980s Invasive Lima et al., 1999; FAO, 2005; Giovanelli et al., 2008; Kraus, 2009; Santos-Barrera et al., 2009Atlantic Rainforest biodiversity hotspot
-BahiaPresentIntroducedLima et al., 1999
-CearaPresentIntroducedLima et al., 1999
-Espirito SantoPresentIntroducedLima et al., 1999
-GoiasPresentIntroducedLima et al., 1999
-Mato Grosso do SulPresentIntroducedLima et al., 1999
-Minas GeraisPresentIntroducedLima et al., 1999
-ParaPresentIntroducedLima et al., 1999
-ParaibaPresentIntroducedLima et al., 1999
-ParanaPresentIntroducedLima et al., 1999
-PernambucoPresentIntroducedLima et al., 1999
-Rio de JaneiroPresentIntroducedLima et al., 1999
-Rio Grande do NortePresentIntroducedLima et al., 1999
-Rio Grande do SulPresentIntroduced Invasive Lima et al., 1999; Kaefer et al., 2007
-Santa CatarinaPresentIntroducedLima et al., 1999
-Sao PauloPresentIntroducedLima et al., 1999
ChilePresentIntroduced Invasive Kraus, 2009
ColombiaPresentIntroduced1986Kraus, 2009; Santos-Barrera et al., 2009Middle Magdalena Valley, north to the lowlands on the Caribbean coast. Also found in Bogotá
EcuadorPresentIntroducedlate 1990sTeixeira et al., 2001; FAO, 2005; Kraus, 2009; Santos-Barrera et al., 2009
GuyanaPresentIntroducedKraus, 2009
PeruLocalisedIntroducedKraus, 2009; Santos-Barrera et al., 2009Established around Iquitos in central Loreto Department in the Amazon Basin, and also around Lima on the Pacific Coast
UruguayLocalisedIntroduced Invasive Teixeira et al., 2001; FAO, 2005; Laufer et al., 2008; Santos-Barrera et al., 2009Introduced in Rincón de Pando, Canelones
VenezuelaLocalisedIntroduced1990sKraus, 2009; Santos-Barrera et al., 2009An expanding population near La Azulita, in Mérida State

Europe

AustriaAbsent, formerly presentIntroducedKraus, 2009
BelgiumPresentIntroduced1980s & 1990sZavod Symbiosis, 2005; Kraus, 2009; Santos-Barrera et al., 2009
DenmarkAbsent, formerly presentIntroduced1990sKraus, 2009
FranceWidespreadIntroducedlate 1800s to 2002 Invasive Touratier, 1992a; Touratier, 1992b; DIAS, 2004; Lichfield, 2005; Ficetola et al., 2007; Kraus, 2009; Santos-Barrera et al., 2009First released near Libourne then spread all over department of the Gironde, to Landes, Dordogne, Lot-et-Cher. Populations in southwest are expanding at an alarming rate
GermanyPresentIntroduced1911 to early 1990s Invasive Zavod Symbiosis, 2005; Kraus, 2009; Santos-Barrera et al., 2009
GreeceLocalisedIntroduced1997Zavod Symbiosis, 2005; Kraus, 2009; Santos-Barrera et al., 2009Crete
ItalyPresentIntroduced1935 - 1970s Invasive Touratier, 1992b; Zavod Symbiosis, 2005; Kraus, 2009
NetherlandsPresentIntroduced1986Zavod Symbiosis, 2005; Kraus, 2009
Russian FederationPresentIntroducedKraus, 2009
SpainPresentIntroduced1880s & 2000 Not invasive Kraus, 2009; Santos-Barrera et al., 2009
UKLocalisedIntroduced1905 & 1996Banks et al., 2000; Marland, 2003; CABI Bioscience et al., 2005; Zavod Symbiosis, 2005; Kraus, 2009England in East Essex and Sussex - Kent border. One discovered at a home in the Scottish Borders in 2003. Patchy records from Hampshire

History of Introduction and Spread

Top of page

In the late 19th and early 20th centuries bullfrogs were translocated from the eastern United States to many western states (Moyle, 1973; Bury and Whelan, 1984) and Hawaii (Pitt et al., 2005), western Canada (Orchard, 1999), the Caribbean (Kairo et al., 2003; Kraus, 2009), western Europe (Ficetola et al., 2007 -- see electronic appendix to this paper for a table with details of introductions to several European countries, mostly in the late 20th century; Lanza, 1962; Veenvliet and Veenvliet, 2003, 2004; Nehring and Klingenstein, 2008), South America (Hanselmann et al., 2004; Giovanelli et al., 2008; Laufer et al., 2008; Kraus, 2009) east Asia (Fei et al., 1999; Hirai, 2004; Wu et al., 2005; Wang et al., 2008) and southeast Asia (Hardouin, 1997). There have also been introductions to western and central Mexico, from the eastern USA and north-eastern Mexico.

Historically the primary motive for moving bullfrogs from place to place has been to profitably cultivate them for human consumption, but there have also been many releases for less obvious reasons. There are currently websites offering to ship bullfrog tadpoles anywhere in the United States ostensibly to enliven backyard ponds. The development of irrigation networks, reservoirs, sewage settling ponds, golf course ponds, farm ponds, and man-made ponds in public parks will permit bullfrogs to take hold in many urban and semi-urban situations and this also facilitates their subsequent dispersal.

Introductions

Top of page
Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Argentina Brazil 1982 Aquaculture (pathway cause)Private sector No Yes DIAS (2004)
Brazil 1935 Aquaculture (pathway cause)Unknown No No Lima and Agostinho (1995)
British Columbia USA Animal production (pathway cause) ,
Aquaculture (pathway cause) ,
Aquarium trade (pathway cause) ,
Breeding and propagation (pathway cause) ,
Escape from confinement or garden escape (pathway cause) ,
Hunting, angling, sport or racing (pathway cause) ,
Intentional release (pathway cause) ,
Pet trade (pathway cause) ,
Research (pathway cause)
Yes No
China Cuba 1982 Aquaculture (pathway cause)Unknown Yes No DIAS (2004)
Cuba 1915 Aquaculture (pathway cause)Unknown Yes No Teixeira et al. (2001)
France Fisheries (pathway cause)Unknown Yes No DIAS (2004)
Indonesia Aquaculture (pathway cause)Government No No DIAS (2004)
Japan 1928 Aquaculture (pathway cause)Unknown Yes No Teixeira et al. (2001)
Korea, Republic of Japan Aquaculture (pathway cause)Government Yes No DIAS (2004)
Malaysia Aquaculture (pathway cause)Unknown No No Teixeira et al. (2001)
Mexico Aquaculture (pathway cause)Unknown No No Teixeira et al. (2001)
Mexico USA Yes No
Puerto Rico 1935 Unknown No No
Taiwan Japan 1924 Aquaculture (pathway cause)Unknown No No Teixeira et al. (2001)
Thailand Aquaculture (pathway cause)Unknown Yes No DIAS (2004)
Uruguay Aquaculture (pathway cause)Unknown No No Teixeira et al. (2001)

Risk of Introduction

Top of page

People continue to routinely transport bullfrogs from one place to another because they appear to be an easily cultivated and profitably marketable commodity for human consumption. Bullfrogs almost inevitably escape because they are, if not impossible, then certainly impractical to confine (see Liu and Lee (2009) for information on the effects of enclosure type and other factors on the risk of escape). However even in the face of wide recognition that it is not a good thing to do, some people persist in moving this ecologically damaging species from place to place for a complex of reasons that range from genuine ignorance to wilful mischief.      

Bullfrogs are behaviourally and physiologically adaptable to a variety of habitats and temperature regimes. Thriving populations of thousands of individuals can arise within the first 12 months of colonization and after only a single successful spawning. Particularly in nutrient-poor (oligotrophic) ponds the algae-eating and rapidly growing bullfrog tadpoles can quite suddenly monopolize primary production (Pryor, 2003), though they are not strictly vegetarian but essentially opportunistic and adaptable omnivores that readily exploit abundant vegetation (Altig et al., 2007). At metamorphosis they convert from primarily vegetarian tadpoles to exceptionally unspecialized carnivores; prey selection above and below the water surface is determined largely by the size of potential prey and whether or not it can be swallowed. Bullfrogs also cannibalize their own tadpoles and juveniles.

Habitat

Top of page

Bullfrogs will colonize a wide variety of lakes, ponds, reservoir, irrigation ditches and marshes, but there are vital characteristics for supporting a population. Permanent water is necessary because bullfrog tadpoles generally take at least 12 months and as much as 48 months to reach metamorphosis; seasonal or intermittent pools, though useful as way stations for migrating bullfrogs, will probably not permit successful reproduction. Water temperature is also important because bullfrogs reproduce only in very warm water when summer temperatures exceed 25 degrees Celsius. For this reason, lakes and ponds that are not too deep < 6 m) and have good sun-exposure around the margins provide most favourable habitat for bullfrog reproduction. Riparian thickets and an abundance of aquatic and emergent vegetation are other factors that, while not vital, are often associated with thriving bullfrog populations because they provide cover and likely a more diverse prey base. However, golf course ponds with edges denuded of most riparian plants can also support healthy bullfrog populations. Acidification of waterways has been associated with bullfrog population declines in southern Ontario (Berrill et al., 1992), but the tolerance limits of bullfrogs to water chemistry extremes and various synthetic chemicals are still being explored.

Habitat List

Top of page
CategoryHabitatPresenceStatus
Freshwater
Irrigation channels Present, no further details Harmful (pest or invasive)
Lakes Principal habitat Harmful (pest or invasive)
Ponds Principal habitat Harmful (pest or invasive)
Reservoirs Principal habitat Harmful (pest or invasive)
Rivers / streams Present, no further details Harmful (pest or invasive)
Terrestrial-natural/semi-natural
Riverbanks Present, no further details
Wetlands Present, no further details

Biology and Ecology

Top of page

Genetics

Recent studies have looked at genetic markers to try to identify the geographical origin, number of founders, and number of introductions of alien, invasive bullfrog populations (Ficetola et al, 2008a; Austin et al., 2004). While this line of research has demonstrated success at achieving its scientific goal, it has not yet been applied to bullfrog management and eradication. These studies do highlight the fact that American bullfrogs are physiologically adaptable and behaviourally flexible when moved between environments that are markedly dissimilar, and that they can invade huge areas starting from only a small number of founder individuals.

Genetic evidence has also been used to investigate gender-biased dispersal in the bullfrog (Austin et al., 2003a), and to detect the presence or absence of bullfrogs by simply analysing a tablespoon of pond water for DNA emanating from mucus, faeces, urine, or decomposing bodies (Ficetola et al., 2008b). 
 
Reproductive biology
 
Bullfrogs reach sexual maturity about 2 years after metamorphosis. Breeding size males attract females by advertising their location through vocalizations. To spawn, a male positions himself on the female’s back and grasps her with his forearms around the anterior thorax or axillary region. This positioning of the male relative to the female at spawning is called axillary amplexus, and is just one of many positions exhibited by frogs (Duellman and Trueb, 1986). The male has ‘nuptial pads’ of roughened skin on the outer edges of the thumbs to assist in holding on to slippery females. Once paired off they ‘spawn’ as fish do with a passive simultaneous release of eggs and sperm whereby fertilization is external. The eggs are very small, dark, and coated in proteins that immediately begin to bond with water molecules to form a protective jelly- and water-filled egg capsule. The egg mass can be anywhere from the size of a small watermelon to over 1 metre across. It is generally anchored in aquatic vegetation in shallow water and floats at the surface. The eggs usually hatch in 3 to 5 days (Bury and Whelan, 1984), but can hatch in as little as 48 hours at 26° Celsius or above (FAO, 2005).
 
Physiology and phenology
 
At higher latitudes bullfrogs mostly overwinter in the water, resting in a physiologically torpid state on the bottom of lakes and ponds where they remain until temperatures rise again in the spring. Bullfrogs are not freeze-tolerant but can withstand temperatures near to freezing. Adults become torpid in the autumn before the juveniles and at higher temperatures. Juveniles also emerge first in the spring and at lower temperatures than adults. Bullfrogs are capable of over-wintering in damp situations on land and should be able to survive quite well provided they can avoid freezing temperatures. In north temperate populations the active season for the adults can be as short as five months, but in the tropics and subtropics bullfrogs remain active year-round. In northerly populations there is a lag period after spring emergence before bullfrogs reproduce, which generally coincides with rising water temperatures to 25° Celsius and above. The spawning season is initiated by mature males finding a territory to defend and then announcing this with their vocalizations. Females then move towards the males to select mates, but not en masse (Ryan 1980). At higher latitudes, e.g. British Columbia, the spawning season lasts about 90 days and coincides with mid to late summer. Further south in the Mississippi drainage the reproductive season is three months in length, and in the tropical climates of Panama and Ecuador, bullfrogs commonly spawn year-round (FAO 2005).                     
 
Nutrition
 
Bullfrog tadpoles mostly graze on aquatic plants, or eat suspended matter, organic debris, algae, plant tissue, and small aquatic invertebrates. After metamorphosis, bullfrogs are carnivorous, and eat any animal (vertebrate or invertebrate) that can be captured and swallowed (including tadpoles and juveniles of their own species).
 
Associations
 
In western North America bullfrogs are often found in association with fish species with which they have co-evolved in the eastern United States. Sunfish, bass, and catfish are all non-native in the western states and western Canada but are now common throughout. The result of this fish/frog association is that the fish can indirectly facilitate bullfrog survival by, for example, depressing the densities of predatory dragonfly nymphs and diving beetle larvae that would otherwise be expected to consume large numbers of larval bullfrogs (Smith et al., 1999; Adams et al., 2003). Bahls (1992) estimates that 95% of western montane lakes and ponds formerly lacked fish, but now virtually all lakes and ponds are stocked with one or more species of non-native fish. Kiesecker and Blaustein (1998) found that when introduced bullfrogs live in association with non-native smallmouth bass (Micropterus dolomieui) they produce an amplified detrimental effect on the growth, development and survival of native red-legged frogs (Rana aurora). The mere presence of bullfrog tadpoles has also been shown to reduce survivorship in both California red-legged frog (R. draytonii, also known as R. aurora draytonii) tadpoles (Lawler et al., 1999) and Columbia spotted frog (Rana luteiventris) tadpoles (Monello et al., 2006). Murray et al. (2004) tested chemical cues from exotic bullfrogs on naive prey species and concluded that some but not all species of naive amphibian prey chemically perceive risk from bullfrog predators and have an avoidance behaviour response. Under laboratory conditions bullfrog tadpoles, in concert with the non-native red swamp crayfish (Procambarus clarkii), have also been shown to eat the eggs and larvae of the endangered razorback sucker (Xyrauchen texanus) in the western United States (Mueller et al., 2006). 
 
At many locations in western North America, bullfrogs are found in association with populations of introduced green frogs, Rana (Lithobates) clamitans, which are also native to eastern North America. Werner et al., (1995) found that in Michigan these two species are able to co-exist even though the bullfrogs prey heavily on juvenile green frogs, because the bullfrogs are primarily aquatic foragers while adult green frogs tend to remain on land within a few metres of the water’s edge.    
 
Beaver ponds have a beneficial effect on bullfrogs by providing new habitat (Cunningham et al., 2007), but beavers are not as widely distributed as they once were. Stock ponds in Tennessee with unrestricted access for cattle were found to support fewer bullfrog tadpoles, presumably due to various negative impacts on water quality by the cattle (Schmutzer et al., 2008).
 
Environmental requirements
 
Bullfrogs require permanent water to reproduce and over-winter, but can utilize seasonal water as way stations to facilitate migration to new lakes and ponds.  Adult bullfrogs require a period of months when the water temperature remains above 17 degrees Celsius and a breeding period when water temperatures rise above 25 degrees Celsius. All age-classes of bullfrogs generally overwinter in the water and require dissolved oxygen concentrations sufficient to drive cutaneous diffusion and maintain aerobic metabolism; they have only a very limited ability to tolerate anoxic conditions (Stewart et al., 2004).

 

Natural Food Sources

Top of page
Food SourceLife StageContribution to Total Food Intake (%)Details
algae Fry
amphibians Adult
aquatic crustaceans Fry
aquatic plants Fry
birds Adult
fishes Adult
insects Adult
mammals Adult
molluscs Adult
reptiles Adult
terrestrial non-insect arthropods Adult
terrestrial worms Adult

Climate

Top of page
ClimateStatusDescriptionRemark
A - Tropical/Megathermal climate Tolerated Average temp. of coolest month > 18°C, > 1500mm precipitation annually
Af - Tropical rainforest climate Tolerated > 60mm precipitation per month
Am - Tropical monsoon climate Tolerated Tropical monsoon climate ( < 60mm precipitation driest month but > (100 - [total annual precipitation(mm}/25]))
Aw - Tropical wet and dry savanna climate Tolerated < 60mm precipitation driest month (in winter) and < (100 - [total annual precipitation{mm}/25])
BS - Steppe climate Tolerated > 430mm and < 860mm annual precipitation
BW - Desert climate Tolerated < 430mm annual precipitation
C - Temperate/Mesothermal climate Tolerated Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C
Cf - Warm temperate climate, wet all year Tolerated Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Tolerated Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter Tolerated Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)
D - Continental/Microthermal climate Tolerated Continental/Microthermal climate (Average temp. of coldest month < 0°C, mean warmest month > 10°C)

Latitude/Altitude Ranges

Top of page
Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
50 33

Water Tolerances

Top of page
ParameterMinimum ValueMaximum ValueTypical ValueStatusLife StageNotes
Ammonia [unionised] (mg/l) <0.5 Optimum Adult
Ammonia [unionised] (mg/l) <0.5 Optimum Egg
Ammonia [unionised] (mg/l) <0.5 Optimum Larval
Ammonia [unionised] (mg/l) <0.5 Optimum Fry
Chloride (mg/l) <7 Optimum Egg
Chloride (mg/l) <7 Optimum Larval
Chloride (mg/l) <7 Optimum Fry
Chlorine (mg/l) 0.02 Optimum Egg
Chlorine (mg/l) 0.02 Optimum Larval
Chlorine (mg/l) 0.02 Optimum Fry
Dissolved oxygen (mg/l) >3 Optimum Wild populations (FAO, 2005)
Hardness (mg/l of Calcium Carbonate) <40 Optimum Adult
Hardness (mg/l of Calcium Carbonate) <40 Optimum Egg
Hardness (mg/l of Calcium Carbonate) <40 Optimum Larval
Hardness (mg/l of Calcium Carbonate) <40 Optimum Fry
Iron (mg/l) <0.3 Optimum Egg
Iron (mg/l) <0.3 Optimum Larval
Iron (mg/l) <0.3 Optimum Fry
Nitrate (mg/l) <1.0 Optimum Adult
Nitrate (mg/l) <1.0 Optimum Egg
Nitrate (mg/l) <1.0 Optimum Larval
Nitrate (mg/l) <1.0 Optimum Fry
Nitrite (mg/l) <0.5 Optimum Adult
Nitrite (mg/l) <0.5 Optimum Egg
Nitrite (mg/l) <0.5 Optimum Larval
Nitrite (mg/l) <0.5 Optimum Fry
Water pH (pH) Optimum May be sensitive to low pH (Berrill et al., 1992)
Water pH (pH) 6.5 7.0 Optimum Adult
Water pH (pH) 6.5 7.0 Optimum Broodstock
Water pH (pH) 6.5 7.0 Optimum Egg
Water pH (pH) 6.5 7.0 Optimum Larval
Water pH (pH) 6.5 7.0 Optimum Fry
Water temperature (ºC temperature) >27 Harmful Adult
Water temperature (ºC temperature) >27 Harmful Broodstock
Water temperature (ºC temperature) >27 Harmful Egg
Water temperature (ºC temperature) >27 Harmful Larval
Water temperature (ºC temperature) >27 Harmful Fry
Water temperature (ºC temperature) 21 27 Optimum Adult
Water temperature (ºC temperature) 21 27 Optimum Broodstock
Water temperature (ºC temperature) 21 27 Optimum Egg
Water temperature (ºC temperature) 21 27 Optimum Larval
Water temperature (ºC temperature) 21 27 Optimum Fry
Water temperature (ºC temperature) 20 35 Optimum 1-42 tolerated (these values apply to wild populations rather than those in culture)

Natural enemies

Top of page
Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Agkistrodon contortrix Predator All Stages
Agkistrodon piscivorus Predator Juvenile/Larval
Alligator mississippiensis Predator All Stages/Larval
Ambystoma tigrinum Predator Egg/Juvenile/Larval
Canis latrans Predator All Stages
Chelydra serpentina Predator Juvenile/Larval
Didelphis virginiana Predator All Stages
Dolomedes triton Predator Larval
Homo sapiens Predator Adult Female/Adult Male
Lutra canadensis Predator All Stages
Mephitis mephitis Predator All Stages
Neovison vison Predator All Stages
Nerodia sipedon Predator All Stages
Procyon lotor Predator All Stages
Rana catesbeiana Predator Juvenile/Larval
Saprolegnia Pathogen Egg
Thamnophis couchi Predator Juvenile/Larval
Thamnophis sauritus septentrionalis Predator Juvenile/Larval

Notes on Natural Enemies

Top of page

Bullfrog eggs are commonly attacked by fungi (Ruthig, 2009) and perhaps leeches (Licht 1969), while the tadpoles are preyed upon by aquatic invertebrates such as dragonfly larvae and predatory water beetles. Although fish sometimes predate bullfrog eggs, tadpoles and juveniles (Bury and Whelan, 1984; Casper and Hendricks, 2005), tadpoles avoid predation by being distasteful to many of the more widespread predatory fish, or use chemical-cued avoidance behaviour in their presence (Pearl et al., 2003). Chemical-cued avoidance behaviour is also used by bullfrog tadpoles in the presence of predatory dragonfly nymphs (Peacor, 2006). Larger aquatic-foraging garter snakes (Thamnophis spp.) might be effective predators of bullfrog tadpoles and juveniles, but garter snakes are commonly eaten by adult bullfrogs. Avian predators include herons and egrets (Ardeidae; Casper and Hendricks, 2005); various reptiles and mammals also eat bullfrogs.

Bullfrogs and their tadpoles have been implicated in the transmission of the pathogenic chytrid fungus Batrachochytrium dendrobatidis (Daszak et al., 2004; Blaustein et al., 2005; Hanselmann et al., 2004; Pearl et al., 2007; they are susceptible to infection, but appear to be immune to the lethal effects experienced by other frog species. Bullfrog tadpoles exposed to chytrid fungus appeared to behave normally (Blaustein et al., 2005). Other pathogens associated with American bullfrogs in recent studies include iridoviruses (Ranavirus), and the bacterium Mycobacterium marinum (Ferreira et al., 2006). Also of interest is the fact that when Kiesecker and Skelly (1999) infected bullfrog tadpoles with the debilitating pathogen Asterotremella humicola (Candida humicola), they found that healthy bullfrog tadpoles avoided infected conspecifics, presumably to reduce the risk of infection. 
 
Limb malformations in frogs, including bullfrogs, have garnered considerable media attention largely due to the initial suspicion that they might be related to deteriorating water quality with potential human health implications (Souder, 2000; Lannoo, 2008). Subsequent research has shown that in many cases these malformations are the result of natural infections by the trematode Ribeiroia, though the incidence of these infections seems to have recently increased (Johnson et al.,2003). Chemical, nutrient and pesticide run-off into wetlands have also been implicated, and all evidence has been comprehensively reviewed by Lannoo (2008).

Means of Movement and Dispersal

Top of page

Bullfrog tadpoles will spread throughout the water bodies in which they have hatched, though they tend to seek out the warmest water. From here they can enter the inflow and outflow waterways that feed and drain lakes and ponds and therefore have a limited ability to migrate. However, because bullfrog larvae (tadpoles) are gill-breathing and entirely aquatic this life stage is unable to move out of the water on its own. 

Near the end of each active season a new generation of bullfrog juveniles, recently transformed from tadpoles, aggregate around lake and pond margins waiting for warm, rainy nights. While the ground surface is wet and under the cover of darkness hundreds to thousands of these juveniles can be seen migrating en masse overland and away from the home lake. Through this risky collective impulse at least some of them will find their way to adjacent lakes and ponds to pioneer new populations. As this activity goes on throughout the late summer and autumn, juveniles seemingly run the risk of being trapped by early frosts. 
 
Natural dispersal (non-biotic)
 
Deluge floods that create sudden or seasonal spillways to interlink otherwise disconnected lakes and ponds could facilitate the dispersal of bullfrog tadpoles and eggs.  
 
Accidental introduction
 
Accidental introductions have occurred where bullfrogs that were meant to be confined as pets or as farm stock have escaped captivity.
 
Intentional introduction
 
Bullfrogs are commonly transported by people.

Pathway Causes

Top of page
CauseNotesLong DistanceLocalReferences
Animal production Yes Yes
Aquaculture Yes Yes
Breeding and propagation Yes Yes
Escape from confinement or garden escape Yes
Hunting, angling, sport or racing Yes Yes
Intentional release Yes Yes
Pet trade Yes Yes
Research Yes Yes
Stocking Yes

Pathway Vectors

Top of page
VectorNotesLong DistanceLocalReferences
Pets and aquarium species Yes Yes
Water Yes

Impact Summary

Top of page
CategoryImpact
Economic/livelihood Positive and negative
Environment (generally) Negative

Economic Impact

Top of page
It is difficult to quantify the economic impact of populations of aggressively invasive bullfrogs. They are known to threaten populations of rare vertebrates such as certain species of turtles, birds and frogs, but it is not clear how this can be translated into economic terms, for example what it is worth to people to save a population or species from extinction, or to save native aquatic ecosystems from an alien invasive that will quickly become one of the dominant species and top predators. Many people are disgusted by the very idea of large bullfrogs swallowing baby ducks or the loss of familiar spring choruses of native frogs, but it is not clear how much they are prepared to spend to have the problem fixed. The summer chorusing of dense aggregations of large male bullfrogs is sometimes identified as a source of noise pollution. However, if this is having a negative effect on real estate values or tourism the damage has yet to be quantified. Aggregations of large bullfrog tadpoles and juveniles at lake edge swimming areas are psychologically disturbing to some people, but it is not clear whether these people will lobby for the funds to have the problem fixed or they simply go swimming elsewhere. There is an interval during the initial stages of a bullfrog invasion when eradication is at its most practical but rapid response is seldom employed and so the cost of eradication becomes increasingly onerous from year to year.

Environmental Impact

Top of page

Bullfrogs are prolific and aggressive competitors for space and voracious predators of a very wide variety of organisms, so displacement of native species is the primary problem that they create (Bury and Whelan, 1984; Lannoo, 2005; Santos-Barrera et al., 2009). They have a much higher critical thermal maximum than most other frogs, meaning that they are able to thrive in higher water temperature, and have a longer breeding season and a higher rate of pre-metamorphic survivorship, which also allows them to be more successful than other frogs. (They also do well with changes in the environment that have occurred due to human modification).

Consequently, their invasions are routinely identified as a principal cause of declining populations of native amphibians (Fisher and Shaffer, 1996; Hecnar and M’Closkey, 1997; Adams, 2000; Kats and Ferrer, 2003; Lannoo et al., 1994; Moyle, 1973; Hammerson, 1982), but questions have been raised about the certainty of some of these claims, as habitat modifications and the introduction of exotic predatory fish and crayfish (Mueller et al., 2006) were concurrent events which can make isolating the effects of invasive bullfrogs difficult to impossible (Hayes and Jennings, 1986). Lannoo et al. (1994) repeated an amphibian survey conducted in 1923 in Dickinson County, Iowa, USA, and concluded that the most immediate threat to the existing populations of native amphibians came from the impact of the introduced bullfrog. Bullfrogs may be a primary predator of several federally endangered waterfowl in Hawaii (Pitt et al., 2005).   Schwalbe and Rosen (1988) concluded that bullfrogs negatively impact populations of native amphibians and reptiles, and at least two species of endangered fish in southeastern Arizona. The presence of bullfrog tadpoles has been shown to reduce survivorship in both California red-legged frog (Rana draytonii, also known as R. aurora draytonii) tadpoles (Lawler et al., 1999) and Columbia spotted frog tadpoles (Monello et al., 2006). Kiesecker and Blaustein (1998) found that the red-legged frog Rana aurora was negatively impacted by bullfrog larvae and adults. Hecnar and M'Closkey (1997) found that Rana clamitans populations increased greatly after bullfrog extirpation at a site in Ontario. Under laboratory conditions bullfrog tadpoles, in concert with the non-native red swamp crayfish (Procambarus clarkii), have also been shown to eat the eggs and larvae of the endangered razorback sucker (Xyrauchen texanus) in the western United States (Mueller et al., 2006).
 
The results of Kupferberg (1997) suggest that invasive bullfrog tadpoles can exert differential effects on native ranid and hylid frogs and perturb aquatic community structure, and Kiesecker et al. (2001) had similar findings when looking at interactions between non-native bullfrog tadpoles and tadpoles of a native ranid. However, Kiesecker et al.(2001) also suggested that human-induced habitat alteration was a key factor in properly interpreting the results. Pearl et al.(2004) confirmed differential effects of introduced bullfrogs on two species of native ranid frogs in the western United States. In Brazil there are no studies on the consequences of bullfrog introduction, although there is news that in several regions bullfrogs have been seen in the wild, near frog farms (Jim, 1995).
 
Further data on the negative impact of bullfrogs on other amphibians are reported by D'Amore et al. (2009 and 2010) (California) and Li et al. (2011) (China).
 
Bullfrogs are known to be asymptomatic carriers of the emerging pathogenic chytrid fungus Batrachochytrium dendrobatidis that has been implicated in numerous amphibian declines and extinctions (Mazzoni et al., 2003; Daszak et al., 2004; Garner et al., 2006; Adams et al., 2007; Sánchez et al., 2008; Schloegel et al., 2009). The fact that bullfrogs and bullfrog meat are transported internationally suggests that bullfrogs may be a primary vector of B. dendrobatidis (Mazzoni et al., 2003). Ranavirus is another pathogen associated with bullfrogs that has been implicated in > 90% mortality rates in free-ranging non-bullfrog amphibians (Daszak et al., 1999; Schloegel et al., 2009) and > 50% mortality amongst bullfrogs in an American ranaculture facility (Miller et al., 2007). A recent outbreak in one pond in western Japan (Une et al., 2009) involved a mass die-off of free-living bullfrog tadpoles, but no dead adult bullfrogs were found. Ranavirus now represents a serious threat to the many endemic amphibians of Japan (Une et al., 2009). There have been significant mortality events reported from bullfrog farming operations involving a variety of pathogenic bacteria (Pasteris et al., 2006). The bacterium Aeromonas hydrophila commonly infects bullfrogs in farms and in nature and the symptomatic syndrome is often called ‘red leg disease’ (Kong et al 1997). 
 
Dense bullfrog populations can also become habitats themselves for many species of internal helminth parasites (McAlpine, 1997; McAlpine and Burt, 1998), and a haemogregarine parasite – Hepatozoon catesbianae – was recently described that appears to be transmitted directly between bullfrogs and mosquitoes (Desser et al., 1995). A trematode was taken from the large intestine of both the western garter snake (Thamnophis elegans) and the American bullfrog with leeches being the intermediate host (Nicol et al, 1985).    

 

Threatened Species

Top of page
Threatened SpeciesConservation StatusWhere ThreatenedMechanismReferencesNotes
Anas bahamensisNo details No detailsPuerto RicoPredationLópez-Flores et al., 2003
Clemmys marmorataNational list(s) National list(s)WashingtonPredationHallock and McAllister, 2005
Rana auroraLC (IUCN red list: Least concern) LC (IUCN red list: Least concern)British ColumbiaPest and disease transmission; PredationHammerson, 2008
Rana draytonii (California Red-legged Frog)VU (IUCN red list: Vulnerable) VU (IUCN red list: Vulnerable); USA ESA listing as threatened species USA ESA listing as threatened speciesCaliforniaPest and disease transmission; PredationHammerson, 2008; US Fish and Wildlife Service, 2002
Rana oncaEN (IUCN red list: Endangered) EN (IUCN red list: Endangered)NevadaPest and disease transmission; PredationBradford et al., 2004
Rana pretiosa (Oregon spotted frog)VU (IUCN red list: Vulnerable) VU (IUCN red list: Vulnerable); USA ESA listing as threatened species USA ESA listing as threatened speciesBritish Columbia; Oregon; WashingtonPest and disease transmission; PredationHammerson and Pearl, 2004
Thamnophis gigas (giant garter snake)VU (IUCN red list: Vulnerable) VU (IUCN red list: Vulnerable); USA ESA listing as threatened species USA ESA listing as threatened speciesCaliforniaPest and disease transmission; PredationHammerson, 2007
Ambystoma californiense (California tiger salamander)VU (IUCN red list: Vulnerable) VU (IUCN red list: Vulnerable); USA ESA listing as endangered species USA ESA listing as endangered speciesCaliforniaPredationUS Fish and Wildlife Service, 2009
Anaxyrus californicus (arroyo toad)EN (IUCN red list: Endangered) EN (IUCN red list: Endangered); USA ESA listing as endangered species USA ESA listing as endangered speciesCaliforniaPredationUS Fish and Wildlife Service, 1999a
Eleutherodactylus cooki (guajon)VU (IUCN red list: Vulnerable) VU (IUCN red list: Vulnerable); USA ESA listing as threatened species USA ESA listing as threatened speciesPuerto RicoPredationUS Fish and Wildlife Service, 2004
Erinna newcombi (Newcomb's snail)VU (IUCN red list: Vulnerable) VU (IUCN red list: Vulnerable); USA ESA listing as threatened species USA ESA listing as threatened speciesHawaiiPredationUS Fish and Wildlife Service, 2006
Gila ditaenia (Sonora chub)VU (IUCN red list: Vulnerable) VU (IUCN red list: Vulnerable); USA ESA listing as threatened species USA ESA listing as threatened speciesArizonaPredationUS Fish and Wildlife Service, 1992
Hyla wrightorum (Arizona treefrog)LC (IUCN red list: Least concern) LC (IUCN red list: Least concern)ArizonaPredationUS Fish and Wildlife Service, 2013b
Kinosternon sonoriense longifemorale (Sonoyta mud turtle)USA ESA species proposed for listing USA ESA species proposed for listingArizonaPredationUS Fish and Wildlife Service, 2013b
Lepidomeda mollispinis pratensis (Big Spring spinedace)USA ESA listing as threatened species USA ESA listing as threatened speciesNevadaPredationUS Fish and Wildlife Service, 1994
Oregonichthys crameri (Oregon chub)LC (IUCN red list: Least concern) LC (IUCN red list: Least concern)OregonPredationUS Fish and Wildlife Service, 1998b
Poeciliopsis occidentalis (Gila topminnow)VU (IUCN red list: Vulnerable) VU (IUCN red list: Vulnerable); USA ESA listing as endangered species USA ESA listing as endangered speciesArizona; New MexicoPredationUS Fish and Wildlife Service, 1998a
Rana chiricahuensis (Chiricahua leopard frog)VU (IUCN red list: Vulnerable) VU (IUCN red list: Vulnerable)ArizonaPredationUS Fish and Wildlife Service, 2007a
Rana muscosa (mountain yellow-legged frog)EN (IUCN red list: Endangered) EN (IUCN red list: Endangered); USA ESA listing as endangered species USA ESA listing as endangered speciesCaliforniaPredationUS Fish and Wildlife Service, 1999b
Rhinichthys osculus lethoporus (Independence Valley speckled dace)USA ESA listing as endangered species USA ESA listing as endangered speciesNevadaPredationUS Fish and Wildlife Service, 2008
Zapus hudsoniusUSA ESA listing as threatened species USA ESA listing as threatened speciesColorado; WyomingPredationUS Fish and Wildlife Service, 2013a

Social Impact

Top of page

There have been cases of severe allergic reaction in some people who ingest the meat of bullfrogs (Hilger et al.,2002). Also, bullfrog tadpoles and metamorphs have been shown to be suitable hosts for the pathogenic bacterium Escherichia coli (Gray et al., 2007). In Japan it was found that 92% of the bullfrogs sampled were highly infected with Blastocystis, a single-celled parasite that infects the gastrointestinal tract of hosts including humans (Yoshikawa et al., 2004). The skinning of bullfrogs has been implicated in rare cases of nematode infection of humans (Quirks and Quarks, CBC Radio, Canadian Broadcasting Corporation). Studies are currently under way looking into whether bullfrogs could play a role in transmission of West Nile virus (WNV), because the virus has been isolated in many amphibian-feeding species of mosquitoes (Klenk and Komar, 2003; Danner & Phillips, 2008). An investigation of a cholera outbreak in Hunan, China, in 2006 concluded that aquatic products such as snapping turtles and bullfrogs constituted the major causes of cholera (Deng et al., 2008).

Risk and Impact Factors

Top of page Invasiveness
  • Invasive in its native range
  • Proved invasive outside its native range
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Is a habitat generalist
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
  • Pioneering in disturbed areas
  • Capable of securing and ingesting a wide range of food
  • Highly mobile locally
  • Benefits from human association (i.e. it is a human commensal)
  • Long lived
  • Fast growing
  • Has high reproductive potential
Impact outcomes
  • Altered trophic level
  • Conflict
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Negatively impacts aquaculture/fisheries
  • Reduced native biodiversity
  • Threat to/ loss of endangered species
  • Threat to/ loss of native species
Impact mechanisms
  • Pest and disease transmission
  • Predation
  • Rapid growth
Likelihood of entry/control
  • Highly likely to be transported internationally deliberately
  • Highly likely to be transported internationally illegally
  • Difficult/costly to control

Uses

Top of page

In many parts of the world where American bullfrogs are non-native, the adults are known to be hunted for food, e.g. in China. It is not known whether this utilization of bullfrogs provides an important dietary supplement or an important source of income, or is simply a recreational activity.

Economic value
 
Trade for human consumption and the pet trade are the two most important forms of trade in amphibians (Daszak et al., 2006). Commercial uses of bullfrogs include supplying frog meat for human consumption, biological supply house specimens for educational dissection, tadpoles and juveniles for pets, and tadpoles for fish bait. There is now a scientific basis for the oft-heard assertion that bullfrogs taste like chicken (Nóbrega et al., 2007), which partly explains why there is a persistent market demand for them.  Bullfrog meat can be either consumed locally as a cheap source of protein or exported to places where it is used as a restaurant novelty or as a traditional menu item in countries like France, Belgium and Luxembourg (United Nations Statistics Division 2008) whose native frog populations are apparently no longer commercially viable. Commercial frog harvesting in France was banned in 1980 (Henley, 2009). Even the United States, where bullfrogs are native, now imports almost all its frogs’ legs (Henley, 2009) and is currently the world’s third top importer. Most are shipped into the United States alive, primarily from Taiwan, followed by Brazil, Ecuador, and China (Schloegel et al., 2009). Indonesia is also one of the world’s largest exporters of frog meat for human consumption, shipping out thousands of tons of native frogs’ legs annually. An experiment in farming American bullfrogs in Indonesia that was initiated in 1982 apparently petered out because of high maintenance costs and vulnerability of bullfrogs to disease (Kusrini and Alford, 2006). Though a number of countries have investigated the viability of commercial culturing of bullfrogs there has so far been little to show for it. Chronic problems that have yet to be solved include nutrition and disease management (Lutz and Avery, 1999). In addition, both semi-natural and artificial systems must deal with predation and cannibalism while rearing an aggressive but fragile amphibian through a complicated life cycle (Lutz and Avery, 1999). Taiwan seems to have been exceptionally successful at producing marketable bullfrogs through aquaculture after a slow start in the 1980s (FAO 2005). 
 
Experiments are currently underway into the aquaculture of native European frogs. These involve the pool frog (Rana lessonae) and the marsh frog (R. ridibunda) as well as a hybrid of the two called the edible frog (R. esculenta [Pelophylax esculenta]). Of these, R. ridibunda has turned out to be the best candidate for farming because it fared best in captivity and reached the target weight of 30 grams. It is proposed that farmed marsh frogs could supply the domestic European market for frogs’ legs and also provide frogs for the re-establishment of populations where they have been extirpated (Barley, 2009; Neveu, 2009), and that a ready supply of domestic frogs’ legs would eliminate any future need for exotic species such as imported and disease-carrying bullfrogs. However, the taxonomic status of European “marsh frogs” is very complex (there is a complex of hybridizing species), and the introduction of  these frogs for aquaculture results in hybridization and extinction of native taxa (Holsbeek et al., 2008). Critics also point out that the fish meal pellets that are fed to these captive frogs are an extravagant drain on declining fish populations (Barley, 2009).
 
As well as their use for food or as pets, bullfrogs are also important for medical research because their skeletal, muscle, digestive, and nervous systems are similar to those of other animals. They also help to control insect pests (University of Michigan Museum of Zoology, 2005).
 
Social benefit
 
There are no identified social benefits to populations of alien, invasive American bullfrogs. They are, however, an iconic species from their native Mississippi drainage and vicinity. 
 
Environmental services
 
Marcogliese et al. (2009) use bullfrogs as their model to point out the importance of parasitism in ecotoxicological studies. Hothem et al. (2009) suggest that due to the bullfrog's widespread abundance in non-native habitats and varied aquatic diet, it should be the species of choice for all lethal biomonitoring of mercury.

Uses List

Top of page

Animal feed, fodder, forage

  • Bait/attractant

General

  • Botanical garden/zoo
  • Capital accumulation
  • Laboratory use
  • Pet/aquarium trade
  • Research model
  • Sport (hunting, shooting, fishing, racing)

Human food and beverage

  • Fresh meat
  • Meat/fat/offal/blood/bone (whole, cut, fresh, frozen, canned, cured, processed or smoked)

Similarities to Other Species/Conditions

Top of page

The average person might find it difficult to distinguish between many species in the widely distributed and speciose family Ranidae (853 described species) because so many of them are green, brown and/or olive-coloured with black irregular patterns. In any case, colour and pattern are not the most reliable of bullfrog characteristics. Size narrows the possibilities where large adult specimens are concerned – a very big specimen is likely to be a bullfrog -- but juvenile bullfrogs can easily be mistaken for other species. The low, sonorous timbre of a male bullfrog’s advertisement call is distinctive compared to that of other frogs. It sounds more in the vocal range of a cow than a frog and amounts to multiple repetitions of “Rrrungh” that vary in volume and intensity depending upon the size of the frog and the temperature of the water in which it is sitting. Juvenile bullfrogs have a distinctive escape behaviour. They produce a characteristic “MEEP” alarm call as they propel themselves into the water when frightened. This action commonly involves skipping over the water surface by rapid multiple kicks of the hind legs before submerging and swimming away.  

The Rana catesbeiana species group consists of seven species found across eastern North America (Austin et al., 2003b), six of which resemble one another to some degree and could therefore be confused with Rana catesbeiana. Unlike most European and North American ranids, such as leopard frogs (Rana (Lithobates) pipiens) and green frogs (Rana (Lithobates) clamitans), bullfrogs do not have a distinctive pair of dorso-lateral ridges. These are thin, straight-edged lines of raised glandular skin tissue that extend from directly behind the eye and above the ear covering (tympanum) and run longitudinally along both upper edges of the back, tapering out toward the upper groin. Bullfrogs do have a slightly protruding fold of skin that extends from just behind the eye and skirts the top and posterior edge of the tympanum.

Prevention and Control

Top of page

Prevention

Bullfrogs are transported by people from place to place, so virtually every means utilized by people to transport themselves and/or their possessions is a de facto means of dispersal for bullfrogs, e.g. aeroplanes, cars, boats, shipping crates, etc. Preventing a determined person from acquiring and transporting eggs, tadpoles, juveniles, or adult bullfrogs from place to place is as complicated as drug enforcement. Education is of some value in making bullfrog problems common knowledge, but this assumes that an informed public will voluntarily be a responsible public. Alternatively, enforced and meaningful penalties for introducing alien species should have some deterrent effect.
 
If bullfrogs are to be farmed, keeping them in secure enclosures at a distance from suitable habitat can reduce, but by no means eliminate, the risk of escape and establishment of feral polulations (Liu and Lee, 2009).
 
When bullfrogs are introduced they quickly make their presence known. The males make a distinctive call. The adults make a loud splash when they jump into the water. All age-classes crave warmth so they are conspicuously active during the day, basking in sunlight. After an initial spawning, thousands of large tadpoles, and later juveniles, crowd the sun-exposed shallows of lakes and ponds. If people can learn to identify bullfrogs by their call and by their appearance, and if they can then be motivated to report what they have seen or heard then a rapid response can be most effective. Responding rapidly is one thing and responding rapidly and effectively is another. Rapid response also requires in advance a plan of exactly what needs to be done and the resources at hand to carry out the plan without delay and on to its logical conclusion. Most jurisdictions currently have a limited budget and poor understanding of what to do. This situation can result in directing the limited money available towards actions such as studying the problem further, writing reports, and launching education campaigns -- none of which will directly address the real need of eradicating a species before it can take hold. The greater the delay in controlling the species, the more it expands.
 
Eradication
 
There is little encouragement to be gleaned from contemporary literature regarding the prospects for successfully eradicating populations of invasive bullfrogs (Adams and Pearl, 2007; Kraus, 2007 & 2009; Pitt et al 2005; Ficetola et al., 2007). Kraus (2009) subjectively rates ‘high rate of reproduction’ as the most constraining factor in controlling or eradicating bullfrogs followed by ‘crypsis’, ‘high density’, and ‘lack of control methods’. There are many examples of both successful (Nehring and Klingenstein, 2008) and unsuccessful eradication efforts (Kraus, 2009), but the successful ones generally seem to apply fairly primitive techniques, e.g. shooting, spearing, netting or fencing, with an extreme intensity of effort at relatively few sites. This approach can result in very expensive operations (Reinhart et al, 2003) that are clearly impractical on a broad regional scale involving multiple lakes and ponds and long-established populations of high density. Consequently, with few success stories to draw from, a conventional dogma has developed that bullfrog eradication is essentially impossible and could be made possible only through the spending of exorbitant and thus prohibitive amounts of money. This line of reasoning seems to discount the possibility of practical innovations coming to the rescue and therefore advises that what little money is available for bullfrog control should go into perpetual public awareness programs, monitoring, and interdiction efforts (Pitt et al., 2005). Unlike ‘eradication’ where there is an end point at which the problem is solved, choosing not to eradicate means that education, monitoring, and interdiction efforts will continue until the public becomes resigned to living with invasive bullfrogs and funding is removed.
 
Bomford and O’Brien (1995), speaking generally about vertebrate eradication programmes, list the following as criteria for a successful eradication: 1) proper planning; 2) socio-political commitment; 3) a removal rate exceeding replacement rate; 4) all individuals being placed at risk; and, 5) prevention of re-invasion. Clout and Veitch (2002) elaborated upon this list with two additional conditions: 1) support from local people; and 2) an ability to demonstrate the benefits of the eradication programme. Unfortunately it is not currently possible to place all individual bullfrogs at risk simultaneously – there is no easy way to round up the eggs and tadpoles in highly vegetated or otherwise obstructed habitats. Thus, the risk to bullfrog tadpoles is deferred until they metamorphose and can be readily located and captured at the surface.   
 
A recent matrix model analysis by Govindarajulu et al. (2005) asserts that eradication programs that target adult bullfrogs will have the detrimental effect of increasing the survivorship of metamorphs by removing cannibalism as a control factor. They further recommend that targeting recent metamorphs in the autumn and egg masses in the spring would be the most profitable approach. Kraus (2009) points out that this notion has yet to be field tested. Schlaepfer et al.(2005) have proposed fast-tracking the evolution of native frog species by carefully exposing them to selective pressures that would drive an evolutionary change in their behaviour relative to the bullfrog predator, e.g. increased escape speed or increased predator detection ability. Their second management approach would then be to inoculate ‘naive’ native populations with individuals from ‘experienced’ populations.
 
Bullfrog invasions are not stemmed by half measures but there are modest actions that can be taken to improve the time efficiency of an eradication program. For example, keeping lake and pond margins free of debris and excessive vegetation that can impede manoeuvrability and visibility from the water will help to speed up the process of locating and capturing bullfrogs, and even when site eradication has been completed these measures will continue to assist the on-going process of monitoring and surveillance to prevent re-colonization.
 
Containment/zoning
 
When bullfrogs appeared in a pond in England in 1996, seven ponds were enclosed behind a barrier fence to prevent the post-metamorphic age-classes from escaping before they could be caught. Twelve thousand bullfrogs were ultimately removed, but at least some of the ponds were eventually filled in which hardly qualifies this as an entirely successful or eco-friendly eradication method (Banks et al.2000; Kraus 2009), as the hope is that a primary goal of bullfrog eradication is to save the habitat for returning native species. In any case, many lakes and ponds would be impossible to easily contain with a barrier fence because of uneven rocky terrain or thick vegetation - and without total containment the exercise is pointless. Containment also needs to take into account that this species can jump nine times its body length, so barriers must be more than a metre high. 
 
Control
 
Although American bullfrogs are labelled as ‘invasive’ – which they are - the primary cause of almost every invasion is ‘translocation’ of bullfrogs by humans. Somehow the ecological problems created by bullfrog invasions and civic responsibilities in the face of bullfrog invasions need to be insinuated into the broader culture. Bullfrogs have a certain charisma and magnetic appeal to the mass media who generally do a more cost-effective job than government in reaching the general public and informing them about the bullfrog problem. Laws should be enacted and enforced that aim to prevent bullfrogs from being transported from place to place. The public needs to be aware of how to identify bullfrogs and where to report sightings; agencies should be prepared to act on these reports, or else the exercise is pointless and the public will feel simply manipulated. There is often community cohesion among people who live around the edges of lakes because of their common interest and investment in the environmental health of the lake. Tapping into these special interest groups can be enormously helpful for intelligence gathering prior to and during eradication and monitoring post-eradication to prevent future re-colonization by bullfrogs. 
 
Physical/mechanical control
There are natural physical barriers to bullfrog dispersal such as thick forest, mountains, deserts, and salt water, and unnatural barriers such as busy highways. However, wherever forests have been cleared and seasonally warm freshwater is available, bullfrogs will invade and it would be very difficult to stop them by any means other than eradication. Mechanical control methods would need to be on the scale of Australia’s rabbit-proof fences, and the cost of such a barrier would far exceed the cost of manually eradicating bullfrog populations. Such barriers, on a small scale, might prevent a generation of juvenile bullfrogs from migrating out of a stock pond or golf course pond, but the barrier would also interfere with the activities of native species that seasonally migrate in and out of ponds and would be likely not to be tolerated by land owners.     
 
Movement control
Bullfrogs are well-recognized internationally as an undesirable alien and appear on the lists of species prohibited for import or translocation. However, this fact has proven to be ineffective in controlling the translocation of bullfrogs by people once the bullfrogs are landed, released and thriving. The best way to prevent translocations thereafter would seem to be to eradicate established populations and put in place rapid response plans to prevent bullfrog populations from becoming re-established. As bullfrog numbers dwindle it can be hoped that the opportunities for and inclinations of people to move them around will also dwindle.
 
Biological control
Natural biological controls on bullfrog numbers range from fungi (Ruthig, 2009) and leeches that attack the egg stage, through dragonfly nymphs and predatory water beetles that prey on newly hatched bullfrog tadpoles, to piscivorous birds and small mammals that eat juvenile and young adult bullfrogs. Where the density of dragonfly nymphs is great they have been shown to be an effective predator of bullfrog tadpoles, but populations of introduced bullfrogs are commonly found in association with introduced predatory fish such as pumpkinseed sunfish (Lepomis sp.) which effectively suppress dragonfly nymph densities through predation. The lesson to be learned from the cases of bullfrogs and cane toads is that when an organism is released into the wild it can have unpredictable and often undesirable results, so the idea of developing or utilizing biological controls such as viruses, bacteria, fungi or predators has inherent dangers that must be approached with extreme caution.    
 
Chemical control
Historically, fisheries agencies have removed so-called ‘non-game’ fish, often referred to as ‘trash fish’ or ‘coarse fish’, from lakes and ponds by poisoning the water with one of a variety of chemical formulations, e.g. toxaphene, antimycin, or activated rotenone. This technique has sometimes been referred to as ‘lake rehabilitation’. Since the larval stage of bullfrogs is entirely aquatic and takes anywhere from 12 to 48 months to reach metamorphosis, this technique would effectively kill one or more generations of tadpoles in a single treatment. It is unlikely that this form of chemical control would have much effect on adult or juvenile bullfrogs because they are able to leave the water and go somewhere else or return later. In any event, there are broad ecological consequences to this form of chemical control because it is also lethal to a host of non-target organisms. Thus, chemical control is not recommended except in the most dire circumstances or where bullfrogs are virtually the only species present during the application of the toxin.
 
Some chemicals released into the environment as fertilizers or pesticides could indirectly increase mortality of bullfrogs at any of their life stages. Conversely, some pesticides and contaminants are apparently harmless to bullfrog embryos and tadpoles (Pauli et al., 1999), and others can indirectly benefit bullfrogs by suppressing the densities of their predators (Boone and Semlitsch 2003) while not harming the bullfrogs. Malformations and decreased swimming performance have been noted in bullfrog tadpoles exposed to potentially toxic trace elements associated with coal combustion (Hopkins et al., 2000). The commonly available pesticide malathion may delay development of bullfrog tadpoles by decreasing thyroid function, but beyond this effect Fordham et al. (2001) found that it took unusually high concentrations to produce any other overt behavioural symptoms such as loss of equilibrium posture. When the popular pesticide Sevin was tested on bullfrog tadpoles in combination with cues from predators it was found to be 46 times more deadly than in tests excluding predator cues (Pelley, 2004).
 
Harvesting/hunting
It is often suggested that permitting and encouraging the harvesting of bullfrogs for human consumption would be an efficient way to control their numbers. However, there are many practical reasons why this approach will not work. For example, if a market demand for bullfrog meat or a recreational interest in hunting them is created, this becomes an argument for sustaining populations rather than eradicating them. Juvenile bullfrogs, the most abundant post metamorphic age-class, are of little interest to hunters because they have relatively little meat on them. Similarly, the egg and tadpole stages are of no interest to meat hunters. 
 
Another prevalent notion is to control bullfrog numbers by offering a bounty on them, but this could have serious adverse consequences. For example, it introduces an untrained work force that may not be able to discriminate between invasive bullfrogs and native frogs and may do great damage to sensitive habitats; there are legal liability issues to consider if people are prompted to wander into treacherous habitats; and there is a mercenary incentive to catch bullfrogs elsewhere and bring them for profit to the region where the bounty is paid.
 
Monitoring and surveillance
 
It is essential at the planning stage of an eradication program to have up-to-date knowledge of the regional limits of bullfrog distribution. Various low-tech methods of surveying for the presence of bullfrogs are very effective, e.g. listening for calling males, searching pond margins, etc. (Heyer et al.,1994). Some high-tech methods such as sampling water for bullfrog DNA or remote-sensing listening stations have also been developed, but remain costly and therefore impractical for broad application.   Monitoring and surveillance are also required after a population has been eradicated to prevent a subsequent re-colonization through bullfrog migration or capture and release by humans. However, on-going monitoring and surveillance programs that are not components of comprehensive eradication programs but are carried out for their own sake are difficult to justify. While the actual eradication of bullfrog populations is best left to professionals, post-eradication monitoring and surveillance can often be turned over to willing volunteers, particularly lakeside residents. 
 
Ecosystem restoration
 
Once a lake or pond is cleared of all life-stages of bullfrogs, many native species that may have been extirpated by the presence of bullfrogs are likely to find their way back on their own if bullfrog-free habitats have persisted nearby. In the bullfrog’s own native range, Hecnar and M’Closkey (1997) reported a four-fold increase in green frog (Rana clamitans) numbers once the bullfrogs were gone. In California, D’Amore et al.(2009) reported a marked increase in the numbers of California red-legged frogs (Rana draytonii, also known as R. aurora draytonii) within the first year of bullfrog removal. There are various case studies where bullfrog removal has been carried out on a relatively small scale as part of a larger wildlife habitat restoration project (Morrison et al. 1994).
 
It is possible to manage areas designed for human recreation, e.g. golf course ponds, so that the survival of non-native bullfrogs and introduced predatory fish is reduced to the point where native amphibian assemblages can flourish (Boone et al. 2008). Intermittent draining of ponds is one way to accomplish this, and the results of Maret et al. (2006) suggest that manipulation or restoration of natural disturbance regimes may be a powerful tool in managing for native species threatened by biotic invasions.

 

Gaps in Knowledge/Research Needs

Top of page

There is a nearly universal agreement that American bullfrogs are one of the worst alien invasive species internationally. They are ecologically destructive and therefore eradication is acknowledged as the most desirable goal. However, there is also a collective sense of defeatism permeating all recent published discussions concerning bullfrog management (Adams and Pearl, 2007; Kraus, 2009). Adams and Pearl (2007) conclude that the “lack of obvious economic impacts” and a lack of reasonably feasible control methods inevitably translate into a lack of political will to supply the resources for large-scale management. Kraus (2009) lists some apparently successful eradication case studies that have been carried out in Europe, but then concludes that these may be exceptions to the general pattern of eradication failure. However, Kraus also observes that large-scale ecological problems are beyond the capabilities and outside the skill sets of the average volunteer organization or institutional research lab, though these are most often the people who are expected to take the initiative. In fact, eradication programs are more akin to military operations. The strategies, tactics and techniques for an effective eradication are to out-flank, out-pace, and ultimately to overwhelm your foe. Traditionally, biologists are trained to study a problem, collect data, and publish results but eradication is something quite different in the degree of dedication and improvisation required. It also needs sufficient long-term commitments from funding agencies as well as adequate support staff.      

The largest gap then, with respect to knowledge/research needs, has been the lack of a reasonably feasible control method and case studies that unambiguously demonstrate success in applying the method. Beyond feasibility, practicality and affordability must be considered. It is currently difficult to quantify what it is worth to people to have populations of invasive bullfrogs controlled or eradicated. Bullfrog choruses may affect property values, or bullfrog predation may threaten the existence of native species in and around lakes and ponds, or aggregations of thousands of tadpoles and juvenile bullfrogs at swimming beaches may be intolerable to some swimmers. It is unclear, however, what is it worth to the people concerned to carry out a total eradication, and what the political profit is in championing the solving of an environmental problem before success is assured. Politicians are often more likely to fund a short-term project than a long-term one. Many conclusions on the prospects for eradication success have been based on subjective or statistical assumptions and deficient data.

References

Top of page

Adams MJ, 2000. Pond permanence and the effects of exotic vertebrates on anurans. Ecological Applications, 10(2):559-568.

Adams MJ, Galvan S, Reinitz D, Cole RA, Pyare S, Hahr M, Govindarajulu P, 2007. Incidence of the fungus Batrachochytrium dendrobatidis in amphibian populations along the northwest coast of North America. Herpetological Review, 38(4):430-431.

Adams MJ, Pearl CA, 2007. Problems and opportunities managing invasive bullfrogs: is there any hope? In: Biological Invaders in Inland Waters: Profiles, Distribution, and Threats [ed. by Gherardi, F.]., The Netherlands: Springer, 679-693.

Adams MJ, Pearl CA, Bury RB, 2003. Indirect facilitation of an anuran invasion by non-native fishes. Ecology Letters, 6:343-351.

Akmentins MS, Cardozo DE, 2010. Invasion note: American bullfrog Lithobates catesbeianus (Shaw, 1802) invasion in Argentina. Biological Invasions, 12(4):735-737. http://dx.doi.org/10.1007/s10530-009-9515-3

Albinati RCB, Lima SL, Tafuri ML, Donzele JL, 2000. Digestibilidade aparente de dois alimentos protéicos e três energéticos para girinos de rã-touro (Rana catesbeiana, Shaw, 1802). R. Bras. Zootec., 29(6):2154-2156.

Altig R, Whiles MR, Taylor CL, 2007. What do tadpoles really eat? Assessing the trophic status of an understudied and imperiled group of consumers in freshwater habitats. Freshwater Biology, 52:386-395.

Austin JD, Dávila JA, Lougheed SC, Boag PT, 2003. Genetic evidence for female-biased dispersal in the bullfrog, Rana catesbeiana (Ranidae). Molecular Ecology, 12:3165-3172.

Austin JD, Lougheed SC, Boag PT, 2004. Controlling for the effects of history and nonequilibrium conditions in gene flow estimates in northern bullfrog (Rana catesbeiana) populations. Genetics, 168:1491-1506.

Austin JD, Lougheed SC, Moler PE, Boag PT, 2003. Phylogenetics, zoogeography, and the role of dispersal and vicariance in the evolution of the Rana catesbeiana (Anura: Ranidae) species group. Biological Journal of the Linnean Society, 80:601-624.

Bahls P, 1992. The status of fish populations and management of high mountain lakes in the western United States. Northwest Science, 66:183-193.

Baker N, 2009. American bullfrog. American bullfrog. Ecology Asia website, unpaginated. http://www.ecologyasia.com/

Banks B, Foster J, Langton T, Morgan K, 2000. British bullfrogs? British Wildlife, (June 2000):327-330.

Barley S, 2009. Intensive frog farming takes giant leap forward. New Scientist. http://www.newscientist.com/article/dn17717-intensive-frog-farming-takes-giant-leap-forward.html

Bee MA, 2003. Experience-based plasticity of acoustically evoked aggression in a territorial frog. Journal of Comparative Physiology A: Neuroethology, Sensory, Neural & Behavioral Physiology, 189(6):485-496.

Bee MA, Gerhardt HC, 2001. Neighbour-stranger discrimination by territorial male bullfrogs (Rana catesbeiana). Animal Behaviour, 62(6):1129.

Berrill M, Bertram S, Tosswill P, Campbell V, 1992. Is there a bullfrog decline in Ontario? In: Declines in Canadian amphibian populations: designing a national monitoring strategy. Workshop Proceedings [ed. by Bishop, C. A.\Pettit, K. E.]. Ottawa, Canada: Canadian Wildlife Service, 32-36. [Occasional Paper Number 76.]

Blaustein AR, Romansic JM, Scheessele EA, Han BA, Pessier AP, Longcore JE, 2005. Interspecific variation in susceptibility of frog tadpoles to the pathogenic fungus Batrachochytrium dendrobatidis. Conservation Biology, 19(5):1460-1468. http://www.blackwell-synergy.com/servlet/useragent?func=showIssues&code=cbi

Boatright-Horowitz SL, Horowitz SS, Simmons AM, 2000. Patterns of vocal interactions in a bullfrog (Rana catesbeiana) chorus: preferential responding to far neighbors. Ethology, 106:701-712.

Bomford M, O'Brien P, 1995. Eradication or control for vertebrate pests? Wildlife Society Bulletin, 23:249-255.

Boone MD, Semlitsch RD, 2003. Interactions of bullfrog tadpole predators and an insecticide: predation release and facilitation. Oecologia, 137(4):610-616.

Boone MD, Semlitsch RD, Mosby C, 2008. Suitability of golf course ponds for amphibian metamorphosis when bullfrogs are removed. Conservation Biology, 22(1):172-179. http://www.blackwell-synergy.com/loi/cbi

Bradford DF, Jaeger JR, Jennings RD, 2004. Population status and distribution of a decimated amphibian, the relict leopard frog (Rana onca). Southwestern Naturalist, 49(2):218-228.

Bury RB, Whelan JA, 1984. Ecology and management of the bullfrog. USFWS Resource Pub., 155:1-23.

CABI Bioscience, Centre for Environment Fisheries and Aquaculture Science (CEFAS), Centre for Ecology and Hydrology (CEH), Central Science Laboratory (CSL), Imperial College London (IC), University of Greenwich (UoG), 2005. North American bullfrog - Rana catesbeiana Shaw, 1802. UK non-native organism risk assessment scheme, version 3.3. Sand Hutton, UK: GB Non-native Species Secretariat, 9 pp.

CaliforniaHerps, 2005. Rana catebeiana-American Bullfrog. Online at www.californiaherps.com/frogs/frogs.html. Accessed 1 June 2005.

Casper GS, Hendricks R, 2005. Rana catesbeiana Shaw, 1802: American bullfrog. In: Amphibian Declines: The Conservation Status of United States Species [ed. by Lannoo, M.]. Berkeley and Los Angeles, California, USA: University of California Press, 540-546.

Clout MN, Veitch CR, 2002. Turning the tide of biological invasion: the potential for eradicating invasive species. Proceedings of the international conference on eradication of island invasives. IUCN Species Survival Commission. [Occasional Paper of the IUCN Species Survival Commission No. 27.]

Collins JT, Taggart TW, 2009. Standard common and current scientific names for North American amphibians, turtles, reptiles, and crocodilians. Sixth edition. Lawrence, USA: Center for North American Herpetology, iv + 44 pp.

CONABIO, 2008. Information system on invasive species in Mexico. (Sistema de información sobre especies invasoras en México.) Information system on invasive species in Mexico. Mexico: CONABIO (National commission for knowledge and use of biodiversity), unpaginated. http://www.conabio.gob.mx/invasoras

Costa CLS, Lima SL, Andrade DR, Agostinho CA, 1998. Morphological characterization of the stages of development of the male reproductive tract in bullfrogs (Rana catesbeiana) reared using an intensive amphibian farming system. Revista Brasileira de Zootecnia, 27(4):651-657.

Costa CLS, Lima SL, Andrade DR, Agostinho CA^circumflex~, 1998. Morphological characterization of the stages of development of the female reproductive tract in bullfrogs (Rana catesbeiana) reared using an intensive amphibian farming system. Revista Brasileira de Zootecnia, 27(4):642-650.

Culley Jr DD, Meyers SP, 1972. Frog culture and ration development. Feedstuffs, 44(31):26-27.

Cunningham JM, Calhoun AJK, Glanz WE, 2007. Pond-breeding amphibian species richness and habitat selection in a beaver-modified landscape. Journal of Wildlife Management, 71(8):2517-2526. http://jwm.allentrack.net

D'Amore A, Hemingway V, Wasson K, 2010. Do a threatened native amphibian and its invasive congener differ in response to human alteration of the landscape? Biological Invasions, 12(1):145-154. http://www.springerlink.com/content/943k084q8265210q/fulltext.html

D'Amore A, Kirby E, McNicholas M, 2009. Invasive species shifts ontogenetic resource partitioning and microhabitat use of a threatened native amphibian. Aquatic Conservation: Marine and Freshwater Ecosystems, 19(5):534-541. http://www3.interscience.wiley.com/journal/122243560/abstract

Danner BA, Phillips CA, 2008. West Nile virus: a serosurvey of ranid frogs across Illinois. Transactions of the Illinois State Academy of Science, 101(1/2):87-94.

Daszak P, Berger L, Cunningham AA, Hyatt AD, Green DE, Speare R, 1999. Emerging infectious diseases and amphibian population declines. Emerging Infectious Diseases, 5(6):735-748.

Daszak P, Schloegel L, Maranda L, Cronin A, Pokras M, Smith K, Picco A, 2006. The global trade in amphibians: summary interim report of a CCM study. The global trade in amphibians: summary interim report of a CCM study. Consortium for Conservation Medicine (CCM), 7 pp.

Daszak P, Strieby A, Cunningham AA, Longcore JE, Brown CC, Porter D, 2004. Experimental evidence that the bullfrog (Rana catesbeiana) is a carrier of chytridiomycosis, an emerging fungal disease in amphibians. Herpetological Journal, 14:201-207.

Deng ZhiHong, Hu ShiXiong, Gao LiDong, Zhang ZhiFei, 2008. Analysis of results in surveillance of cholera in Hunan in 2006. Disease Surveillance, 23(3):147-149. http://www.jbjc.org

Desser SS, Hong H, Martin DS, 1995. The life history, ultrastructure, and experimental transmission of Hepatozoon catesbianae n. comb., an apicomplexan parasite of the bullfrog, Rana catesbeiana and the mosquito, Culex territans in Algonquin Park, Ontario. Journal of Parasitology, 81(2):212-222.

DIAS, 2004. FAO Database on Introductions of Aquatic Species. Online at www.fao.org/figis/. Accessed 25 February 2005.

Duellman WE, Trueb L, 1986. Biology of amphibians. Baltimore, USA: The John Hopkins University Press, 670 ppp.

Emlen ST, 1976. Lek organization and Mating strategies in the bullfrog. Behavioral Ecology and Sociobiology, 1:283-313.

FAO, 2005. Rana catesbeiana (Shaw, 1802). Cultured aquatic species information programme. Rome, Italy: FAO Fisheries and Aquaculture Department, unpaginated. http://www.fao.org/fishery/culturedspecies/Rana_catesbeiana/en

Fei L, Ye CY, Huang YA, Liu MY, 1999. Atlas of amphibians of China [ed. by Liang, F.]., China: Henan Science and Technology, 432 pp.

Ferreira R, Fonseca L de S, Afonso AM, Silva MG da, Saad MH, Lilenbaum W, 2006. A report of mycobacteriosis caused by Mycobacterium marinum in bullfrogs (Rana catesbeiana). Veterinary Journal, 171(1):177-180.

Ficetola GF, Bonin A, Miaud C, 2008. Population genetics reveals origin and number of founders in a biological invasion. Molecular Ecology, 17(3):773-782. http://www.blackwell-synergy.com/loi/mec

Ficetola GF, Claude M, Francois P, Pierr T, 2008. Species detection using environmental DNA from water samples. Biology Letters, 4(4):423-425.

Ficetola GF, Coïc C, Detaint M, Berroneau M, Lorvelec O, Miaud C, 2007. Pattern of distribution of the American bullfrog Rana catesbeiana in Europe. Biological Invasions, 9(7):767-772. http://dx.doi.org/10.1007/s10530-006-9080-y

Fisher RN, Shaffer HB, 1996. The decline of amphibians in California's Great Central Valley. Conservation Biology, 10:1387-1397.

Fordham CL, Tessari JD, Ramsdell HS, Keefe TJ, 2001. Effects of malathion on survival, growth, development, and equilibrium posture of bullfrog tadpoles (Rana catesbeiana). Environmental Toxicology and Chemistry, 20(1):179-184.

Frost DR, 2009. Amphibian species of the world: an online reference, Version 5.3. New York, USA: American Museum of Natural History, unpaginated. http://research.amnh.org/vz/herpetology/amphibia/

Frost DR, Grant T, Faivovich J, Bain RH, Haas A, Haddad CFB, Sà RO De, Channing A, Wilkinson M, Donellan SC, Raxworthy CJ, Campbell JA, Blotto BL, Moler P, Drewes RC, Nussbaum RA, Lynch JD, Green DM, Wheeler WC, 2006. The amphibian tree of life. Bulletin of the American Museum of Natural History, 297:1-291.

Gans C, 1974. Biomechanics. Philadelphia, USA: J. B. Lippincott Co., 272 pp.

Garner TWJ, Perkins MW, Purnima Govindarajulu, Seglie D, Walker S, Cunningham AA, Fisher MC, 2006. The emerging amphibian pathogen Batrachochytrium dendrobatidis globally infects introduced populations of the North American bullfrog, Rana catesbeiana. Biology Letters, 2(3):455-459. http://www.pubs.royalsoc.ac.uk/biol_lett

Giovanelli JGR, Haddad CFB, Alexandrino J, 2008. Predicting the potential distribution of the alien invasive American bullfrog (Lithobates catesbeianus) in Brazil. Biological Invasions, 10(5):585-590. http://www.springerlink.com/content/e7n8737568n69134/?p=895847694ede4683a2f9efc3c78f7aa7&pi=0

Govindarajulu P, Altwegg R, Anholt BR, 2005. Matrix model investigation of invasive species control: bullfrogs on Vancouver Island. Ecological Applications, 15(6):2161-2170. http://www.esajournals.org/perlserv/?request=get-abstract&doi=10.1890%2F05-0486

Gray MJ, Rajeev S, Miller DL, Sehmutzer AC, Burton EC, Rogers ED, Hickling GJ, 2007. Preliminary evidence that American bullfrogs (Rana catesbeiana) are suitable hosts for Escherichia coli O157:H7. Applied and Environmental Microbiology, 73(12):4066-4068. http://aem.asm.org

Green DM, 2007. Arguments, counter-arguments and general mystification over new scientific names for amphibians. The Boreal Dip Net, 11(2):7-8.

Hallock LA, McAllister KR, 2005. Western pond turtle. Washington Herp Atlas. unpaginated. http://www.dnr.wa.gov/nhp/refdesk/herp/

Hammerson GA, 1982. Amphibians and reptiles in Colorado. Colorado Division of Wildlife, Denver, 131 pp.

Hammerson GA, 2007. Thamnophis gigas. IUCN 2009. IUCN Red List of Threatened Species, Version 2009.2. unpaginated. http://www.iucnredlist.org

Hammerson GA, 2008. Rana aurora. IUCN 2009. IUCN Red List of Threatened Species, Version 2009.2. unpaginated. http://www.iucnredlist.org

Hammerson GA, Pearl C, 2004. Rana pretiosa. IUCN 2009. IUCN Red List of Threatened Species, Version 2009.2. unpaginated. http://www.iucnredlist.org

Hanselmann R, Rodríguez A, Lampo M, Fajardo-Ramos L, Aguirre AA, Kilpatrick AM, Rodríguez JP, Daszak P, 2004. Presence of an emerging pathogen of amphibians in introduced bullfrogs Rana catesbeiana in Venezuela. Biological Conservation, 120(1):115-119.

Hardouin J, 1991. A bull-frog rearing enterprise in the Philippines. (Un élevage de grenouilles-tareaux aux Philippines.) Tropicultura, 9(1):34-36.

Hardouin J, 1997. Commercial production of frogs in Malaysia. (Elevage commercial de grenouilles en Malaisie.) Tropicultura, 15(4):209-213.

Hayes MP, Jennings MR, 1986. Decline of ranid frog species in western North America: are bullfrogs (Rana catesbeiana) responsible? J. Herpetol., 20:490-509.

Hecnar SJ, M’Closkey RT, 1997. Changes in the composition of a ranid frog community following bullfrog extinction. American Midland Naturalist, 137:145-150.

Henley J, 2009. Why we shouldn't eat frogs' legs. The Guardian. http://www.guardian.co.uk

Heyer WR, Donnelly MA, McDiarmid RW, Hayek LAC, Foster MS, 1994. Measuring and monitoring biological diversity: standard methods for amphibians., USA: Smithsonian Institution Press, 364 pp. [Biological Diversity Handbook Series.]

Hilger C, Grigioni F, Thill L, Mertens L, Hentges F, 2002. Severe IgE-mediated anaphylaxis following consumption of fried frog legs: definition of alpha-parvalbumin as the allergen in cause. Allergy, 57(11):1053-1058.

Hirai T, 2004. Diet composition of introduced bullfrog, Rana cateseiana, in the Mizorogaike Pond of Kyoto, Japan. Ecological Research, 19:375-380.

Holsbeek G, Mergeay J, Hotz H, Plötner J, Volckaert FAM, Meester L de, 2008. A cryptic invasion within an invasion and widespread introgression in the European water frog complex: consequences of uncontrolled commercial trade and weak international legislation. Molecular Ecology, 17(23):5023-5035. http://www.blackwell-synergy.com/loi/mec

Hopkins WA, Ray JK, Congdon J, 2000. Incidence and impact of axial malformations in larval bullfrogs (Rana catesbeiana) developing in sites polluted by a coal-burning power plant. Environmental Toxicology & Chemistry, 19(4):862.

Hothem RL, Meckstroth AM, Wegner KE, Jennings MR, Crayon JJ, 2009. Diets of three species of anurans from the Cache Creek Watershed, California, USA. Journal of Herpetology, 43(2):275-283.

Hou PingChun [Hou PCL], Shiau TsuWay, Tu MingChung, Chen ChingChi, Chen TungYu, Tsai YaFen, Lin ChunFu, Wu ShengHai, 2006. Exotic amphibians in the pet shops of Taiwan. Taiwania, 51(2):87-92. http://tai2.ntu.edu.tw/taiwania

ISSG, 2005. Global Invasive Species Database (GISD). University of Auckland, New Zealand. http://www.issg.org/database

Jim J, 1995. Ecologia das rãs. In: Proceedings of the First International Meeting on Frog Research and Technology, February 1995. Viçosa – MG, Brasil: ABETRA/UFV, 167-190.

Johnson PTJ, Lunde KB, Zelmer DA, Kirwin WJ, 2003. Limb deformities as an emerging parasitic disease in amphibians: evidence from museum specimens and resurvey data. Conservation Biology, 17(6):1724-1737.

Kaefer ÍL, Boelter RA, Cechin SZ, 2007. Reproductive biology of the invasive bullfrog Lithobates catesbeianus in southern Brazil. Annales Zoologici Fennici, 44(6):435-444. http://www.sekj.org/PDF/anz44-free/anz44-405.pdf

Kairo M, Ali B, Cheesman O, Haysom K, Murphy S, 2003. Invasive species threats in the Caribbean region. Report to the Nature Conservancy. Curepe, Trinidad and Tobago: CAB International, 132 pp. http://www.issg.org/database/species/reference_files/Kairo%20et%20al,%202003.pdf

Kats LB, Ferrer RP, 2003. Alien predators and amphibian declines: review of two decades of science and the transition to conservation. Diversity and Distributions, 9:99-110.

Kellog R, 1932. Mexican Tailless Amphibians in the United States National Museum. Bulletin of the U.S. National Museum, Number 160.

Kiesecker JM, Blaustein AR, 1997. Population differences in responses of red-legged frogs (Rana aurora) to introduced bullfrogs. Ecology, 78(6):1752.

Kiesecker JM, Blaustein AR, 1998. Effects of introduced bullfrogs and smallmouth bass on microhabitat use, growth, and survival of native red-legged frogs (Rana Aurora). Conservation Biology, 12:776-787.

Kiesecker JM, Blaustein AR, Miller CL, 2001. Potential mechanisms underlying the displacement of native red-legged frogs by introduced bullfrogs. Ecology, 82(7):1964.

Kiesecker JM, Skelly DK, 1999. Behavioural reduction of infection risk. Proceedings of the National Academy of Sciences of the United States of America, 96(16):9165.

Klenk K, Komar N, 2003. Poor replication of West Nile virus (New York 1999 strain) in three reptilian and one amphibian species. American Journal of Tropical Medicine and Hygiene, 69(3):260-262.

Kong FanDe, Huang YinYao, Wu WenZhong, Chen Qiong, 1997. Isolation and identification of two strains of Aeromonas. Chinese Journal of Veterinary Science and Technology, 27(2):23-24.

Kraus F, 2007. Using pathway analysis to inform prevention strategies for alien reptiles and amphibians. In: Managing Vertebrate Invasive Species: Proceedings of an International Symposium [ed. by Witmer, G. W.\Pitt, W. C.\Fagerston, K. A.]. Fort Collins, Colorado, USA: USDA/APHIS/WS, National Wildlife Research Center, 94-103.

Kraus F, 2009. Invading nature: Springer series in invasion ecology 4. Springer, 563 pp.

Krupa JJ, 2002. Temporal shift in diet in a population of American bullfrog (Rana catesbeiana) in Carlsbad Caverns National Park. The Southwest Naturalist, 47(3):461-467.

Kupferberg SJ, 1997. Bullfrog (Rana catesbeiana) invasion of a California river: the role of larval competition. Ecology, 78(6):1736.

Kusrini MD, Alford RA, 2006. Indonesia's exports of frogs' legs. TRAFFIC Bulletin, 21(1):13-28.

Lannoo M, 1995. Summary report of American bullfrog questionnaire. Summary report of American bullfrog questionnaire.

Lannoo M, 1996. Okoboji wetlands: a lesson in natural history. Iowa City, USA: University of Iowa Press, 156 pp.

Lannoo M, 2005. Amphibian declines: the conservation status of United States species. Berkeley and Los Angeles, California, USA: University of California Press, 1094 pp.

Lannoo M, 2008. Malformed frogs: the collapse of aquatic ecosystems. Berkeley, USA: University of California Press, 270 pp.

Lannoo M, Lang K, Waltz T, Phillips GS, 1994. An altered amphibian assemblage: Dickinson County, Iowa, 70 years after Frank Blanchard's survey. American Midland Naturalist, 131(2):311-319.

Lanza B, 1962. On the introduction of Rana ridibunda Pallas and Rana catesbeiana Shaw in Italy. Copeia, 1962(3):642-643.

Laufer G, Canavero A, Núñez D, Maneyro R, 2008. Bullfrog (Lithobates catesbeianus) invasion in Uraguay. Biological Invasions, 10:1183-1189.

Lawler SP, Dritz D, Strange T, Holyoak M, 1999. Effects of introduced mosquitofish and bullfrogs on the threatened California red-legged frog. Conservation Biology, 13(3):613-622.

Li YiMing, Ke ZhunWei, Wang YiHua, Blackburn TM, 2011. Frog community responses to recent American bullfrog invasions. Current Zoology, 57(1):83-92. http://www.actazool.org/temp/%7B85541E8B-C331-46FD-BF8C-BFF82D9AF9F4%7D.pdf

Li YiMing, Wu ZhengJun, Duncan RP, 2006. Why islands are easier to invade: human influences on bullfrog invasion in the Zhoushan archipelago and neighboring mainland China. Oecologia, 148(1):129-136. http://springerlink.metapress.com/content/e517540q4723645v/?p=bda584b4849c4f1887ff51ad81bb580f&pi=13

Lichfield J, 2005. French countryside hit by a massive invasion of frogs. The Independent (World Section).

Licht LE, 1969. Palatability of Rana and Hyla eggs. American Midland Naturalist, 82:292-298.

Lima SL, Agostinho CA, 1988. A criação de rãs. Rio de Janeiro: Globo, 187pp.

Lima SL, Agostinho CA, 1995. A tecnologia de criação de rãs. Viçosa: Impr. Univ., 166pp.

Lima SL, Casali AP, Agostinho CA, 2003. Performance and food intake of bullfrogs (Rana catesbeiana) during the post-metamorphic stage in the "Amphifarm" system. Revista Brasileira de Zootecnia, 32(3):505-511.

Lima SL, Casali AP, Agostinho CA, 2003. Performance of bullfrog tadpoles (Rana catesbeiana) raised in the "Amphifarm" system and feeding tables. Revista Brasileira de Zootecnia, 32(3):512-518.

Lima SL, Cruz TA, Moura OM, 1999. Ranicultura: análise da cadeia produtiva. Viçosa: Ed. Folha fr Viçosa, 172 pp.

Liu X, Li YM, 2009. Aquaculture enclosures relate to the establishment of feral populations of introduced species. PLoS ONE, 4:E6199.

López-Flores M, Cruz-Burgos JA, Vilella FJ, 2003. Predation of a white-cheeked pintail (Anas bahamensis) duckling by a bullfrog (Rana catesbeiana). Caribbean Journal of Science, 39(2):240-242.

Lowe S, Browne M, Boudjelas S, Poorter M De, 2000. 100 of the world's worst invasive alien species: a selection from the global invasive species database. 100 of the world's worst invasive alien species: a selection from the global invasive species database. The Invasive Species Specialist Group (ISSG), Species Survival Commission (SSC), World Conservation Union (IUCN), 12 pp. http://www.issg.org/pdf/publications/worst_100/english_100_worst.pdf

Lutz CG, Avery JL, 1999. Bullfrog culture. SRAC Publications, No. 436. Southern Regional Aquaculture Center (SRAC), 4 pp. http://www.msstate.edu/dept/srac/publicat.htm

Mahon R, Aiken K, 1977. The establishment of the North American bullfrog, Rana catesbeiana (Amphibia, Anuira, Ranidae) in Jamaica. Journal of Herpetology, 11(2):197-199.

Marcantonio AS, Lui JF, Stéfani MV, 2002. Estudo citogenético da rã-touro (Rana catesbeiana Shaw, 1802). Ars Veterinária, 18(2):174-178.

Marcogliese DJ, King KC, Salo HM, Fournier M, Brousseau P, Spear P, Champoux L, McLaughlin JD, Boily M, 2009. Combined effects of agricultural activity and parasites on biomarkers in the bullfrog, Rana catasbeiana. Aquatic Toxicology, 91(2):126-134. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T4G-4TNWGR5-2&_user=10&_coverDate=01%2F31%2F2009&_rdoc=6&_fmt=high&_orig=browse&_srch=doc-info(%23toc%234974%232009%23999089997%23838052%23FLA%23display%23Volume)&_cdi=4974&_sort=d&_docanchor=&_ct=13&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=67724a034995fc33dd5986d7f4e226a9

Maret TJ, Snyder JD, Collins JP, 2006. Altered drying regime controls distribution of endangered salamanders and introduced predators. Biological Conservation, 127(2):129-138.

Marland I, 2003. Giant Bullfrogs Still Being Imported. Giant bullfrogs still being imported. unpaginated. http://lists.envirolink.org/pipermail/ar-news/Week-of-Mon-20031013/008327.html

Mazzoni R, Cunningham AA, Daszak P, Apolo A, Perdomo E, Speranza G, 2003. Emerging pathogen of wild amphibians in frogs (Rana catesbeiana) farmed for international trade. Emerging Infectious Diseases, 9(8):995-998.

McAlpine DF, 1997. Helminth communities in bullfrogs (Rana catesbeiana), green frogs (Rana clamitans), and leopard frogs (Rana pipiens) from New Brunswick, Canada. Canadian Journal of Zoology, 75(11):1883-1890.

McAlpine DF, Burt DB, 1998. Helminths of bullfrogs, Rana catesbeiana, green frogs, R. clamitans, and leopard frogs, R. pipiens in New Brunswick. Canadian Field-Naturalist, 112:50-68.

McKercher L, Gregoire DR, 2009. Lithobates [Rana] catesbeianus. USGS Nonindigenous Aquatic Species Database. Gainsville, Florida, USA: United States Geological Survey, unpaginated. http://nas.er.usgs.gov/

Miller DL, Rajeev S, Gray MJ, Baldwin CA, 2007. Frog virus 3 infection, cultured American bullfrogs. Emerging Infectious Diseases, 13(2):342-343. http://www.cdc.gov/eid

Monello RJ, Dennehy JJ, Murray DL, Wirsing AJ, 2006. Growth and behavioral responses of tadpoles of two native frogs to an exotic competitor, Rana catesbeiana. Journal of Herpetology, 40(3):403-407.

Morrison ML, Scott TA, Tennant T, 1994. Wildlife-habitat restoration in an urban park in Southern California. Restoration Ecology, 2(1):17-30.

Moyle PB, 1973. Effects of introduced bullfrogs, Rana catesbeiana, on the native frogs of the San Joaquin Valley, California. Copeia, 1973(1):18-22.

Mueller GA, Carpenter J, Thornbrugh D, 2006. Bullfrog tadpole (Rana catesbeiana) and red swamp crayfish (Procambarus clarkii) predation on early life stages of endangered razorback sucker (Xyrauchen texanus). The Southwestern Naturalist, 51(2):258-261.

Murray DL, Roth JD, Wirsing AJ, 2004. Predation risk avoidance by terrestrial amphibians: the role of prey experience and vulnerability to native and exotic predators. Ethology, 110:635-647.

NatureServe, 2005. Comprehensive Report Species – Rana catesbeiana. Online at www.natureserve.org/explorer/. Accessed 1 June 2005.

Nehring S, Klingenstein F, 2008. Aquatic alien species in Germany - listing system and options for action. In: Biological Invasions - from Ecology to Conservation [ed. by Rabitsch, W.\Essl, F.\Klingenstein, F.]. Berlin, Germany: NEOBIOTA, 19-33. [NEOBIOTA 7.]

Neveu A, 2009. Suitability of European green frogs for intensive culture: comparison between different phenotypes of the esculenta hybridogenetic complex. Aquaculture, 295(1/2):30-37. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T4D-4WMM7CW-1&_user=10&_coverDate=10%2F01%2F2009&_rdoc=6&_fmt=high&_orig=browse&_srch=doc-info(%23toc%234972%232009%23997049998%231432085%23FLA%23display%23Volume)&_cdi=4972&_sort=d&_docanchor=&_ct=22&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=45b718f98a9ed5a21221ae50e69589d0

Nicol JT, Demaree R Jr, Wootton DM, 1985. Levinseniella (Monarrhenos) ophidea sp.n. (Trematoda: Microphallidae) from the western garter snake, Thamnophis elegans and the bullfrog, Rana catesbeiana. Proceedings of the Helminthological Society of Washington, 52(2):180-183.

Nóbrega ICC, Ataíde CS, Moura OM, Livera AV, Menezes PH, 2007. Volatile constituents of cooked bullfrog (Rana catesbeiana) legs. Food Chemistry, 102(1):186-191. http://www.sciencedirect.com/science/journal/03088146

Orchard SA, 1999. The American bullfrog in British Columbia: the frog who came to dinner. In: Nonindigenous Freshwater Organisms: Vectors, Biology, and Impacts [ed. by Claudi, R.\Leach, J. H.]. Lewis Publishers, 289-296.

Pasteris SE, Bühler MI, Nader-Macías ME, 2006. Microbiological and histological studies of farmed-bullfrog (Rana catesbeiana) tissues displaying red-leg syndrome. Aquaculture, 251(1):11-18. http://www.sciencedirect.com/science/journal/00448486

Pauli BD, Coulson DR, Berrill M, 1999. Sensitivity of amphibian embryos and tadpoles to Mimic® 240 LV insecticide following single or double exposures. Environmental Toxicology and Chemistry, 18(11):2538-2544.

Pauly GB, Hillis DM, Cannatella DC, 2009. Taxonomic freedom and the role of official lists of species names. Herpetologica, 65(2):115-128.

Peacor SD, 2006. Behavioural response of bullfrog tadpoles to chemical cues of predation risk are affected by cue age and water source. Hydrobiologia, 2006(573):39-44.

Pearl CA, Adams MJ, Bury RB, McCreary B, 2004. Asymmetrical effects of introduced bullfrogs (Rana catesbeiana) on native ranid frogs in Oregon. Copeia, 2004(1):11-20.

Pearl CA, Adams MJ, Schuytema GS, Nebeker AV, 2003. Behavioral responses of anuran larvae to chemical cues of native and introduced predators in the Pacific Northwestern United States. Journal of Herpetology, 37(3):572-576.

Pearl CA, Bull EL, Green DE, Bowerman J, Adams MJ, Hyatt A, Wente WH, 2007. Occurrence of the amphibian pathogen Batrachochytrium dendrobatidis in the Pacific Northwest. Journal of Herpetology, 41(1):145-149. http://www.bioone.org/perlserv/?request=get-document&doi=10.1670%2F0022-1511%282007%2941%5B145%3AOOTAPB%5D2.0.CO%3B2

Pelley J, 2004. Natural stresses magnify pesticide's side effects. Environmental Science & Technology, 38(5):83A-84A.

Pitt WC, Vice DS, Pitzler ME, 2005. Challenges of invasive reptiles and amphibians. In: Proceedings of the 11th Wildlife Damage Management Conference, Traverse City, Michigan, USA [ed. by Nolte, D. L.\Fagerstone, K. A.]. Fort Collins, Colorado, USA: Wildlife Damage Management, 112-119.

Pryor GS, 2003. Growth rates and digestive abilities of bullfrog tadpoles (Rana catesbeiana) fed algal diets. Journal of Herpetology, 37(3):560-566. http://apt.allenpress.com/aptonline/?request=get-abstract&issn=0022-1511&volume=037&issue=03&page=0560

Purgue AP, 1997. Tympanic sound radiation in the bullfrog, Rana catesbeiana. Journal of Comparative Physiology A, 181:438-445.

Reinhardt F, Herle M, Bastiansen F, Streit B, 2003. Economic impact of the spread of alien species in Germany. Federal Environmental Agency, Research Report: 201 86 211 UBA-FB 000441e. Germany: Federal Environmental Agency.

Rogers CP, 1996. Natural history notes: Rana catesbeiana (bullfrog). Predation. Herpetological Review, 27:19.

Ruthig GR, 2009. Water molds of the genera Saprolegnia and Leptolegnia are pathogenic to the North American frogs Rana catesbeiana and Pseudacris crucifer, respectively. Diseases of Aquatic Organisms, 84(3):173-178. http://www.int-res.com/abstracts/dao/v84/n3/p173-178/

Ryan MJ, 1980. The reproductive behavior of the bullfrog (Rana catesbeiana). Copeia, 1980:108-114.

Sanabria E, Debandi G, Quiroga L, Martínez F, Corbalán V, 2011. First record of the American bullfrog Lithobates catesbeianus (Shaw, 1802) in Mendoza province, Argentina. Cuadernos de Herpetología, 25(2):55-58.

Sanabria E, Ripoll Y, Jordan M, Quiroga L, Ariza M, Guillemain M, Pérez M, Chávez H, 2011. A new record for American Bullfrog (Lithobates catesbeianus) in San Juan, Argentina. Revista Mexicana de Biodiversidad, 82:311-313.

Sanabria EA, Quiroga LB, Acosta JC, 2005. Introduction of Rana catesbeiana Shaw (bullfrog) in pre-Andean environments of San Juan province, Argentina. (Introducción de Rana catesbeiana Shaw (rana toro), en ambientes precordilleranos de la Provincia de San Juan, Argentina.) Multequina, 14:67-70.

Sánchez D, Chacón-Ortiz A, León F, Han BA, Lampo M, 2008. Widespread occurrence of an emerging pathogen in amphibian communities of the Venezuelan Andes. Biological Conservation, 141(11):2898-2905. http://www.sciencedirect.com/science/journal/00063207

Santos-Barrera G, Hammerson G, Hedges B, Joglar R, Inchaustegui S, Lue K, Chou W, Gu H, Shi H, Diesmos A, Iskandar D, Dijk PP van, Masafumi M, Schmidt B, Miaud C, Martínez-Solano C, Martínez-Solano I, 2009. Lithobates catesbeianus. In: IUCN Red List of Threatened Species, Version 2009.2. unpaginated. http://www.iucnredlist.org

Schlaepfer MA, Sherman PW, Blossey B, Runge MC, 2005. Introduced species as evolutionary traps. Ecology Letters, 8:241-246.

Schloegel LM, Picco AM, Kilpatrick AM, Davies AJ, Hyatt AD, Daszak P, 2009. Magnitude of the US trade in amphibians and presence of Batrachochytrium dendrobatidis and ranavirus infection in imported North American bullfrogs (Rana catesbeiana). Biological Conservation, 142(7):1420-1426. http://www.sciencedirect.com/science/journal/00063207

Schmutzer AC, Gray MJ, Burton EC, Miller DL, 2008. Impacts of cattle on amphibian larvae and the aquatic environment. Freshwater Biology, 53(12):2613-2625. http://www3.interscience.wiley.com/cgi-bin/fulltext/121355890/HTMLSTART

Schwalbe CR, Rosen PC, 1988. Preliminary report on effect of bullfrogs on wetland herpetofaunas in Southeastern Arizona. In: Proceedings of the symposium: Management of amphibians, reptiles, and small mammals in North America [ed. by Szaro, R. C.\Severson, K. E.\Patton, D. R.]. Fort Collins, Colorado, USA: U. S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station, 166-173. [General Technical Report RM-166.]

Smith GR, Rettig JE, Mittlebach GG, Valiulus JL, Schaack SR, 1999. The effects of fish on assemblages of amphibians in ponds: a field experiment. Freshwater biology, 41:829-837.

Smith HM, Taylor EH, 1948. An annotated checklist and key to the amphibia of Mexico. Bulletin of the U.S. National Museum, Number 194.

Souder W, 2000. A plague of frogs: the horrifying true story. New York, USA: Hyperion, 299 pp.

Stewart ER, Reese SA, Ultsch GR, 2004. The physiology of hibernation in Canadian leopard frogs (Rana pipiens) and bullfrogs (Rana catesbeiana). Physiological and Biochemical Zoology, 77(1):65-73.

Storer TI, Usinger RL, 1965. General Zoology. Fourth edition. McGraw-Hill, 741 pp.

Tan BC, Tan KS, 2002. Invasive alien species in Singapore: a review. ASEAN Biodiversity, October-December 2002:33-34.

Tangley L, 2003. A plague of aliens. National Wildlife, 41(2):42.

Teixeira RD, Pereira Mello SCR, Lima dos Santos CAM, 2001. The world market for frog legs. FAO/GLOBEFISH Research Programme, 68:44 pp.

Touratier L, 1992. Apparent similarities and differences between the feral populations of American bullfrogs (Rana catesbeiana) spreading in Italy and in France. Veterinary public health aspects. (Similitudes et différences acuellement apparentes entre les grenouilles-taureaux (Rana catesbeiana) en voie de propagation en Italie et en France. Émergence des questions de santé publique vétérinaire.) Bulletin Mensuel de la Société Vétérinaire Pratique de France, 76(6-7):349-355.

Touratier L, 1992. First appearance in France (Aquitaine region) of the American bullfrog: Rana catesbeiana, adapting to the French climate. Zoological interest and eventual impact on the environment. (Première apparition en France (Région Aquitaine) d'une grenouille géante Américaine: Rana catesbeiana en voie d'acclimatement. Intérêt zoologique et impact eventuel sur l'environnement.) Bulletin Mensuel de la Société Vétérinaire Pratique de France, 76(4):219-221, 224-228.

Une Y, Sakuma A, Matsueda H, Nakai K, Murakami M, 2009. Ranavirus outbreak in North American bullfrogs (Rana catesbeiana), Japan, 2008. Emerging Infectious Diseases, 15(7):1146-1147. http://www.cdc.gov/eid/content/15/7/1146.htm

United Nations Statistics Division, 2008. Trade of goods, US$, HS 1992, 02 Meat and edible meat offal.

University of Michigan Museum of Zoology, 2005. Animal Diversity Web. Online at http://animaldiversity.ummz.umich.edu/site/index.html. Accessed 1 June 2005.

US Fish and Wildlife Service, 1992. In: Sonora Chub Gila ditaenia Recovery Plan. US Fish and Wildlife Service, 83 pp.. http://ecos.fws.gov/docs/recovery_plan/920930.pdf

US Fish and Wildlife Service, 1994. In: Big Spring Spinedace (Lepidomeda mollispinis pratensis) Recovery Plan. US Fish and Wildlife Service, 51 pp.. http://ecos.fws.gov/docs/recovery_plan/940120.pdf

US Fish and Wildlife Service, 1998. In: Gila Topminnow, Poeciliopsis occidentalis occidentalis, Revised Recovery Plan. US Fish and Wildlife Service, 83 pp..

US Fish and Wildlife Service, 1998. In: Oregon Chub (Oregonichthys crameri) Recovery Plan. US Fish and Wildlife Service, 96 pp.. http://ecos.fws.gov/docs/recovery_plan/980903b.pdf

US Fish and Wildlife Service, 1999. In: Arroyo Southwestern Toad (Bufo microscaphus californicus) Recovery Plan. US Fish and Wildlife Service, 119 pp..

US Fish and Wildlife Service, 1999. In: Endangered and Threatened Wildlife and Plants: Proposed Endangered Status for the Southern California Distinct Vertebrate Population Segment of the Mountain Yellow-Legged Frog. US Fish and Wildlife Service, 9 pp..

US Fish and Wildlife Service, 2002. In: Recovery Plan for the California Red-legged Frog.(Rana aurora draytonii). US Fish and Wildlife Service, 180 pp.. http://ecos.fws.gov/docs/recovery_plan/020528.pdf

US Fish and Wildlife Service, 2004. In: Recovery Plan for the Guajon or Puerto Rican Demon (Eleutherodactylus cooki). US Fish and Wildlife Service, 36 pp.. http://ecos.fws.gov/docs/recovery_plan/040924b.pdf

US Fish and Wildlife Service, 2006. In: Final Recovery Plan for the Newcomb's Snail (Erinna newcombi). US Fish and Wildlife Service, 61 pp.. http://ecos.fws.gov/docs/recovery_plan/060918b.pdf

US Fish and Wildlife Service, 2007. In: Chiricahua Leopard Frog (Rana chiricahuensis) Recovery Plan. US Fish and Wildlife Service, 429 pp.. http://ecos.fws.gov/docs/recovery_plan/070604_v3.pdf

US Fish and Wildlife Service, 2007. In: Vernal Pool Fairy Shrimp 5-Year Review. Summary and Evaluation. US Fish and Wildlife Service, 76 pp.. http://ecos.fws.gov/docs/five_year_review/doc1150.pdf

US Fish and Wildlife Service, 2008. In: Independence Valley Speckled Dace (Rhinichthys osculus lethoporus). 5-Year Review: Summary and Evaluation. US Fish and Wildlife Service, 27 pp..

US Fish and Wildlife Service, 2009. In: California tiger salamander (Ambystoma californiense) Santa Barbara County Distinct Population Segment. 5-Year Review: Summary and Evaluation. US Fish and Wildlife Service, 59 pp.. http://ecos.fws.gov/docs/five_year_review/doc3223.pdf

US Fish and Wildlife Service, 2013. In: Endangered and Threatened Wildlife and Plants; 12-Month Finding on Two Petitions to Delist the Preble's Meadow Jumping Mouse. 78(101) US Fish and Wildlife Service, 31680-31712. http://www.gpo.gov/fdsys/pkg/FR-2013-05-24/pdf/2013-12387.pdf

US Fish and Wildlife Service, 2013. In: U.S. Fish and Wildlife Service species assessment and listing priority assignment form: Hyla wrightorum. US Fish and Wildlife Service, 34 pp.. https://ecos.fws.gov/docs/candidate/assessments/2014/r2/D03S_V02.pdf

US Fish and Wildlife Service, 2014. In: U.S. Fish and Wildlife Service species assessment and listing priority assignment form: Kinosternon sonoriense longifemorale. US Fish and Wildlife Service, 24 pp.. http://ecos.fws.gov/docs/candidate/assessments/2014/r2/C067_V01.pdf

Veenvliet P, Veenvliet JK, 2003. List of European literature on American bullfrogs. List of European literature on American bullfrogs, Version 1.0. Denmark: Amphi Consult, unpaginated. http://www.zavod-symbiosis.si

Veenvliet P, Veenvliet JK, 2004. American bullfrogs (Rana catesbeiana) in Europe. American bullfrogs (Rana catesbeiana) in Europe. Denmark: Amphi Consult, unpaginated. http://www.zavod-symbiosis.si

Villee CA, Walker W, Smith FE, 1963. General Zoology. Third edition. WB Saunders, 844 pp.

Wang Y, Li Y, 2009. Habitat selection by the introduced American bullfrog (Lithobates catesbeianaus) on Daishan Island, China. Journal of Herpetology, 43(2):205-211.

Wang Y, Wang Y, Lu P, Zhang F, Li Y, 2008. Diet composition of post-metamorphic bullfrogs (Rana catesbeiana) in the Zhoushan archipelago, Zhejiang Province, China. Front. Biol. China 2008, 3(2):219-226.

Weller WF, Green DM, 1997. Checklist and current status of Canadian Amphibians. In: Amphibians in decline: Canadian studies of a global problem [ed. by Green, D. M.]. Saint Louis, Missouri, USA: Society for the Study of Amphibians and Reptiles, 309-328. [Herpetological Conservation 1.]

Werner EE, Wellborn GA, McPeek MA, 1995. Diet composition in postmetamorphic bullfrogs and green frogs: implications for interspecific predation and competition. Journal of Herpetology, 29(4):600-607.

Wu Z, Li Y, Wang Y, Adams MJ, 2005. Diet of introduced bullfrogs (Rana catesbeiana): predation on and diet overlap with native frogs on Daishan Island, China. Journal of Herpetology, 39(4):668-674.

Yoshikawa H, Morimoto K, Nagashima M, Miyamoto N, 2004. A survey of Blastocystis infection in anuran and urodele amphibians. Veterinary Parasitology, 122(2):91-102.

Zavod Symbiosis, 2005. Bullfrogs. Online at www.zavod-symbiosis.si/. Accessed 1 June 2005.

Links to Websites

Top of page
WebsiteURLComment
AmphibiaWebhttp://amphibiaweb.org/
BullfrogControl.com.Inchttp://www.bullfrogcontrol.com
FAO: Cultured Aquatic Species Information Programmehttp://www.fao.org/fishery/culturedspecies/Rana_catesbeiana/en
ISSG database global Invasive Species Database)http://www.issg.org
IUCN Red Listhttp://www.redlist.org

Organizations

Top of page

World: Invasive Species Specialist Group (ISSG), Web based, http://www.issg.org/contact.htm

World: IUCN/SSC Global Amphibian Assessment, IUCN/SSC, International, http://www.issg.org

Italy: FAO (Food and Agriculture Organization of the United Nations), Viale delle Terme di Caracalla, 00100 Rome, http://www.fao.org/

Mexico: CONABIO - National Commission for Knowledge and Use of Biodiversity, Liga Periférico - Insurgentes Sur, Núm. 4903, Col. Parques del Pedregal, Delegación Tlalpan, 14010, http://www.conabio.gob.mx

USA: US Geological Survey - USGS, USGS National Center 12201 Sunrise Valley Drive, Reston, VA 20192, http://nas.er.usgs.gov

Contributors

Top of page

08/12/2009 Original text (Invasive Species Compendium) by:

Stan Orchard, BullfrogControl.com Inc., 69A Burnside Road West, Victoria, British Columbia, V9A 1B6, Canada

04/05/2005 Original text (Aquaculture Compendium) by:

Marta Stéfani, Departamento de Zootecnia da FCAV/Unesp Jaboticabal, Via de Ac. Prof. Paulo Donato Castellane, s/n Jaboticabal - SP - 14884-900, Brazil

Distribution Maps

Top of page
You can pan and zoom the map
Save map
Download KML file Download CSV file
Creative Commons Licence
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

Please click OK to ACCEPT or Cancel to REJECT

Creative Commons Licence
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

Please click OK to ACCEPT or Cancel to REJECT