Invasive Species Compendium

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Amynthas agrestis
(crazy worm)

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Datasheet

Amynthas agrestis (crazy worm)

Summary

  • Last modified
  • 17 October 2018
  • Datasheet Type(s)
  • Invasive Species
  • Preferred Scientific Name
  • Amynthas agrestis
  • Preferred Common Name
  • crazy worm
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Annelida
  •       Class: Oligochaeta
  •         Order: Haplotaxida
  • Summary of Invasiveness
  • Amynthas agrestis is an epigeic (litter-dwelling) Asian earthworm. It is native from Japan and the Korean Peninsula and has been introduced to the eastern United States, where it has spread widely, predominantl...

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Pictures

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PictureTitleCaptionCopyright
Amynthas agrestis; immatures. This individual has recently autotomized a posterior section of its body in response to handling. Blount County, Tennessee, USA. June 2005.
TitleImmatures
CaptionAmynthas agrestis; immatures. This individual has recently autotomized a posterior section of its body in response to handling. Blount County, Tennessee, USA. June 2005.
Copyright©Bruce A. Snyder - All Rights Reserved
Amynthas agrestis; immatures. This individual has recently autotomized a posterior section of its body in response to handling. Blount County, Tennessee, USA. June 2005.
ImmaturesAmynthas agrestis; immatures. This individual has recently autotomized a posterior section of its body in response to handling. Blount County, Tennessee, USA. June 2005.©Bruce A. Snyder - All Rights Reserved
Amynthas agrestis; cocoons and a hatchling. Unhatched cocoons have a small amount of soil adhering to their surface. Cocoons were produced in the laboratory by adult individuals from eastern Tennessee, USA. Note mm scale.
TitleCocoons and a hatchling
CaptionAmynthas agrestis; cocoons and a hatchling. Unhatched cocoons have a small amount of soil adhering to their surface. Cocoons were produced in the laboratory by adult individuals from eastern Tennessee, USA. Note mm scale.
Copyright©Bruce A. Snyder - All Rights Reserved
Amynthas agrestis; cocoons and a hatchling. Unhatched cocoons have a small amount of soil adhering to their surface. Cocoons were produced in the laboratory by adult individuals from eastern Tennessee, USA. Note mm scale.
Cocoons and a hatchlingAmynthas agrestis; cocoons and a hatchling. Unhatched cocoons have a small amount of soil adhering to their surface. Cocoons were produced in the laboratory by adult individuals from eastern Tennessee, USA. Note mm scale.©Bruce A. Snyder - All Rights Reserved
Amynthas agrestis; colour variation in cocoons. Cocoons were produced in the laboratory by adult individuals from north Georgia, USA. Note mm scale.
TitleCocoons
CaptionAmynthas agrestis; colour variation in cocoons. Cocoons were produced in the laboratory by adult individuals from north Georgia, USA. Note mm scale.
Copyright©Bruce A. Snyder - All Rights Reserved
Amynthas agrestis; colour variation in cocoons. Cocoons were produced in the laboratory by adult individuals from north Georgia, USA. Note mm scale.
CocoonsAmynthas agrestis; colour variation in cocoons. Cocoons were produced in the laboratory by adult individuals from north Georgia, USA. Note mm scale.©Bruce A. Snyder - All Rights Reserved

Identity

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Preferred Scientific Name

  • Amynthas agrestis (Goto and Hatai, 1899)

Preferred Common Name

  • crazy worm

Local Common Names

  • USA: jumpers; snake worm; wigglers; wood eel

Summary of Invasiveness

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Amynthas agrestis is an epigeic (litter-dwelling) Asian earthworm. It is native from Japan and the Korean Peninsula and has been introduced to the eastern United States, where it has spread widely, predominantly in forests. It has also been recorded from one location in Canada, near the USA border. Introduction and long-distance spread are thought to be associated with either transport of horticultural materials (for greenhouses, nurseries, and planting locations) or release of earthworms used as fishing bait.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Annelida
  •             Class: Oligochaeta
  •                 Order: Haplotaxida
  •                     Genus: Amynthas
  •                         Species: Amynthas agrestis

Notes on Taxonomy and Nomenclature

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The taxonomy of A. agrestis is and has been relatively stable. The species was originally described in the genus Perichaeta (Goto and Hatai, 1899), moved to Pheretima, and finally to Amynthas (Sims and Easton, 1972). Blakemore (2003) briefly and incorrectly listed the species in Metaphire, correcting this in subsequent publications (e.g. Blakemore, 2009).

Description

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The following description is based on the most recent summary of A. agrestis by Chang et al. (2016):

A. agrestis is a moderately sized, surface-dwelling (epigeic) earthworm of adult size 70-160 mm length and 5-8 mm width. Live specimens are red, but often appear somewhat brownish or purplish, with some iridescence. A. agrestis moves in a serpentine motion and will thrash/jump when disturbed, and it will often (but not always) autotomize a posterior body region in defence. As with other Amynthas, the clitellum is pale and surrounds the entire body in segments 14-16, each segment has a ring of many (40 or more) setae (perichaetine) in the middle of the segment. This group of earthworms is identified by using the number and location of sexual pores and swellings (genital markings) on the body and the shape of sexual (spermathecae) and somatic (intestinal caecae) organs. A. agrestis usually lacks male pores and genital markings posterior to the clitellum (both found ventrally in segment 18); when present, the pores are small and slit-like, and the markings are large, circular, slightly concave pads, just anterior and median to the pores. A. agrestis typically has three pairs of spermathecal pores ventrally at the intersegmental furrow between segments 5 & 6, 6 & 7, and 7 & 8, with corresponding spermathecae inside segments 6, 7 and 8. Spermathecal number may be reduced. Genital markings anterior to the clitellum are often absent; when present, these appear as slightly discoloured and wrinkled areas located ventrally in segments 7 and/or 8. These may be single/median or paired. Internally, spermathecae have a duct shorter than the ampulla, with a thin, cylindrical diverticulum that is longer than the combined duct and ampulla (illustrated in Chang et al., 2016). Prostate glands are usually absent but, when present, are found in segment 23, and can extend through segment 16. Paired intestinal caecae have 5-7 finger-shaped divisions (manicate). They branch from the intestine in segment 27 and extend anteriorly for a few segments.

A. agrestis and other species in this group can be challenging to identify due to variability in several characteristics. In case of preserved specimens, identification can be even harder due to poor visibility of specific characteristics because of low quality of preservation. Positive identification of the species requires dissection of an adult specimen for confirmation of location and shape of spermathecae, intestinal caecae, and other structures. As of 2017, for the known species of earthworms in North America north of Mexico, an adult (clitellate) earthworm with all of the following characteristics should be identified as A. agrestis: perichaetine setae, size >50 mm, male pores absent, three pairs of spermathecae. As described above, other combinations of characteristics are also possible, but confirmation of the species would be needed.

Using morphological characteristics, juveniles can only be identified as pheretimoid (Amynthas or related genera). Internal organs grow gradually, thus moderately sized juveniles can sometimes be positively identified with dissection.

Distribution

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The native range of A. agrestis includes the four main islands of Japan and the Korean Peninsula. Following introduction, it is now widespread in eastern North America, from Alabama and Georgia to New Hampshire and Vermont. Additional locations include northern Louisiana, eastern Texas, southeastern Oklahoma (Tandy, 1969; Gates, 1982; Damoff and Reynolds, 2009), one location in Wisconsin (Qiu and Turner, 2017), one in Ontario (Reynolds, 2014) and a greenhouse in Maine (Gates, 1966). While many of these localities consist of natural or managed habitats, such as arboreta (e.g., Gates, 1953), A. agrestis has been recorded in many human-created environments (e.g., culture beds, nurseries, compost heaps; Gates, 1954; 1958; 1963; Reynolds, 1977).

Distribution Table

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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

JapanPresentNative Not invasive Present based on regional distribution
-HokkaidoPresentNative Not invasive Hatai, 1930; Gates, 1953; Gates, 1982Sapporo, Hokkaido
-HonshuPresentNative Not invasive Goto and Hatai, 1899; Hatai, 1930; Gates, 1953; Gates, 1954Aomori Prefecture, Iawati Prefecture, Takahashi, Tokorozawa, Oarai, Sendai, Oshima Island
-KyushuPresentNative Not invasive Hatai, 1930; Gates, 1953Kagoshima, Tomitaka
-ShikokuPresentNative Not invasive Hatai, 1930; Gates, 1953Matsuyama
Korea, DPRPresentNative Not invasive Kobayashi, 1938
Korea, Republic ofPresentNative Not invasive Kobayashi, 1938

North America

CanadaPresentIntroduced Invasive Present based on regional distribution
-OntarioPresentIntroduced Invasive Reynolds, 2014Essex Co.
USAPresentIntroduced Invasive Present based on regional distribution
-AlabamaPresentIntroduced Invasive Reynolds, 1978; Gates, 1982Dallas, Montgomery, and Tuscaloosa Cos.
-ConnecticutPresentIntroduced Invasive Gates, 1958; Gates, 1982Fairfield Co.
-FloridaPresentIntroduced Invasive Gates, 1982Sumter Co.
-GeorgiaPresentIntroduced Invasive Reynolds, 1978; Gates, 1982; Callaham et al., 2003
-KentuckyPresentIntroduced Invasive Gorsuch and Owen, 2014Daniel Boone National Forest - single record in a remote area, needs confirmation
-LouisianaPresentIntroduced Invasive Gates, 1958; Tandy, 1969Widespread north of the Red River
-MainePresentIntroduced Invasive Reynolds, 2008a; Gates, 1966
-MarylandPresentIntroduced Invasive Howell, 1939First North American record
-MassachusettsPresentIntroduced Invasive Gates, 1953; Reynolds, 1977
-MissouriPresentIntroduced Invasive Reynolds, 2008b; Stebbings, 1962
-New HampshirePresentIntroduced Invasive Reynolds et al., 2015Belknap Co.
-New JerseyPresentIntroduced Invasive Davies, 1954
-New YorkPresentIntroduced Invasive Gates, 1954; Gates, 1958; Gates, 1963; Gates, 1982; Bernard et al., 2009
-North CarolinaPresentIntroduced Invasive Reynolds, 1978; Gates, 1982; Reynolds, 1994; Blackmon, 2009
-OhioPresentIntroduced Invasive Reynolds, 2015a; Schermaier, 2013Clinton, Lake, and Summit Cos.
-OklahomaPresentIntroduced Invasive Reynolds, 1978; Gates, 1982McCurtain Co.
-PennsylvaniaPresentIntroduced Invasive Reynolds, 2008c; Bhatti, 1965
-South CarolinaPresentIntroduced Invasive Reynolds, 1978; Gates, 1982Darlington and Jasper Cos.
-TennesseePresentIntroduced Invasive Reynolds, 1978; Snyder et al., 2011
-TexasPresentIntroduced Invasive Damoff and Reynolds, 2009Widespread in east Texas
-VermontPresentIntroduced Invasive Görres and Melnichuk, 2012; Reynolds et al., 2015Present in multiple sites throughout the state
-VirginiaPresentIntroduced Invasive Reynolds, 2015bHenry Co.
-West VirginiaPresentIntroduced Invasive Gates, 1982Summers Co.
-WisconsinPresentIntroduced Invasive Qiu and Turner, 2017Madison, University of Wisconsin - Madison Arboretum

History of Introduction and Spread

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Details of the introduction of A. agrestis into the USA are unknown. Presumably, as is the case for other invasive earthworms, the species was introduced multiple times, with the first introductions occurring before the first A. agrestis record in 1939 (Howell, 1939). Asian earthworm introductions were ongoing at least half a century prior - the first pheretimoid record in North America was from a greenhouse (hot-house) in Illinois, in 1888 (Garman, 1888). Recognising this fact, Howell (1939) speculated about the species route of introduction: “introduced into this country with botanical products imported probably 15 to 20 years ago.” Details of the introduction of A. agrestis to Canada are unknown. The species may have been transported directly from its native range or from the USA.

Early records of the species are all associated with exotic plants. It is thus likely that, as Howell (1939) surmised, the original introduction(s) came with soil or other organic material accompanying plants from Asia. These were then planted in arboreta (Gates, 1953; Qiu and Turner, 2017) or grown in nurseries/culture beds/greenhouses (e.g., Gates, 1958; Gates, 1963). Plants and the earthworms associated with them were then transported and planted at various locations, which contributed to widely dispersing the species (Gates, 1958; Tandy, 1969).

An additional route of dispersal has been through the use of the species as bait for anglers (Gates, 1958). The species has been observed for sale in bait shops (Callaham et al., 2003) and there is evidence that populations have been started intentionally to provide a local source of bait (Tandy, 1969). Many of the invaded natural habitats are near actively fished waters (Tandy, 1969; Callaham et al., 2003; Snyder et al., 2011).

Risk of Introduction

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The routes of introduction/spread mentioned in the 'History of Introduction and Spread' section (horticultural materials and bait) continue to be relevant today and may unknowingly result in new invasions in remote or protected areas (e.g., Callaham et al., 2003; Snyder et al., 2011). The risk of introduction from horticultural materials may extend to any organic matter product associated with horticulture or landscaping, including soil, leaf litter, compost and mulch. Mulch (pieces of shredded wood up to 5 cm) is not an ideal habitat for this species, but survival in/under mulch has been documented and is linked to a high risk for transport and establishment of this species in gardens (Bellitürk et al., 2015).

In addition to local purchase for bait or composting, earthworms purported to be A. agrestis can also be ordered online (Ziemba et al., 2016). Earth-moving activities (e.g., road building) have been shown to act as pathways of introduction and spread for other invasive earthworms, being a potential route of transport for A. agrestis.

Habitat List

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CategorySub-CategoryHabitatPresenceStatus
Terrestrial-managed/Protected agriculture (e.g. glasshouse production) Present, no further details Harmful (pest or invasive)
Terrestrial-managed/Managed forests, plantations and orchards Present, no further details Harmful (pest or invasive)
Terrestrial-managed/Disturbed areas Present, no further details Harmful (pest or invasive)
Terrestrial-managed/Rail / roadsides Present, no further details Harmful (pest or invasive)
Terrestrial-managed/Urban / peri-urban areas Present, no further details Harmful (pest or invasive)
Terrestrial-natural/semi-natural/Natural forests Present, no further details Harmful (pest or invasive)
Terrestrial-natural/semi-natural/Riverbanks Present, no further details Harmful (pest or invasive)
Other/Soil Present, no further details Harmful (pest or invasive)

Biology and Ecology

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Genetics

A. agrestis genetics has been little studied, although interest in using molecular techniques to aid identification has been increasing. Schult et al. (2016) used two loci to examine the genetic divergence of Amynthas spp. and suggest that there may be cryptic speciation. However, morphological identification of some individuals by an expert was able to refer specimens in each lineage to a valid species, only by using species morphology.

Reproductive Biology

All earthworms are hermaphrodites and many, including A. agrestis, have developed parthenogenesis (Gates, 1958; Chang et al., 2016). Thus, most individuals encountered in the native or introduced range lack male pores and/or other parts of the male sexual system. Unlike many earthworms, A. agrestis has an annual life cycle (Tandy, 1969; Reynolds, 1978; Callaham et al., 2003; Chang et al., 2016). They overwinter as cocoons, hatch in spring, reach adulthood in summer, lay cocoons and all adults die by winter. A. agrestis lays spherical or subspherical cocoons of slightly under 2 mm diameter (Snyder et al., 2013). Cocoon colour is variable, from yellow to brown to red. Most cocoons contain one individual, but ~2% contain two individuals (Ikeda et al., 2015). Cocoon viability after 4 months has been shown to be between 60 and 70% (Ikeda et al., 2015). External sexual structures do not develop until near sexual maturity.

Physiology and Phenology

In Japan (Kanagawa Prefecture), A. agrestis juveniles were found in April-May and adults beginning in June (Uchida and Kaneko, 2004). In Louisiana, USA, juveniles were found April-June and adults were present in May-September (Tandy, 1969). In Tennessee, USA, juveniles or aclitellate adults were found May-June and adults were collected in June-December (Reynolds, 1978). Adults collected in September in Tennessee and North Carolina laid cocoons between September and November (Blackmon, 2009). At a high elevation site in north Georgia, USA (~1450m above sea level), juveniles were collected July-September, while adults were collected August-November (Callaham et al., 2003). Similarly, in Vermont, USA adults were observed July-November (Görres et al., 2014).

A. agrestis is known to bioaccumulate heavy metals, particularly Se, Zn, Cd and Hg (Richardson et al., 2015).

Longevity

A. agrestis has a life cycle lasting ~1 year. Little research has monitored the cocoon stage. Development from hatchling to adult is estimated to be a minimum of 90 days, based on frost-free periods of invaded locations (Görres and Melnichuk, 2012). Although, in the field, adults die in late fall or early winter, they have been kept alive in the laboratory through February (Snyder et al., 2013; Ikeda et al., 2015).

Nutrition

Soil and litter both play a large role in the biology of A. agrestis. Soil is a requirement for survival, weight maintenance and reproduction: in mesocosms with no soil (leaf litter only), A. agrestis lost weight and died, producing no cocoons (Ikeda et al., 2015). In this same study, A. agrestis with only soil survived, lost more weight than treatments with both litter and soil, and produced a limited number of cocoons. A. agrestis performs better on partially-decomposed leaf litter over fresh leaves, and appears to derive some nutrition from soil (Snyder et al., 2013; Ikeda et al., 2015). A combination of all three substrates provided the best nutrition (Ikeda et al., 2015). Zhang et al. (2010) found that A. agrestis feeds more on soil than Lumbricus rubellus (an epigeic European species also introduced in the USA) and, when needed, can shift its feeding strategy to more available soil or litter microbes.

A. agrestis can also survive in soil with mulch on top. Bellitürk et al. (2015) found that, in addition to survival and maturation over a 7 week incubation period with spruce, cedar, or pine mulch, A. agrestis increased lignin-digesting enzyme activity (phenoloxidase and peroxidase) in these soils. Mortality rates in this experiment were 10-30%, but there was no control against which to measure the effect of mulch on this variable.

Environmental Requirements

In the laboratory, adult A. agrestis did not survive at soil temperatures of -5, 5 or 35°C, but did survive at 12 and 25°C; moisture played a role, with no survival at 8% moisture and 25°C, but higher survival in wetter soils at the same temperature (Richardson et al., 2009). Field studies in Vermont indicate that 5°C may not be a minimum threshold temperature and that specimen size may play a role (Görres et al., 2014). Görres and Melnichuk (2012) suggest that the frost-free period (air temperature) may be an important predictor of A. agrestis tolerance of a site, because of time required to mature.

Temperature may play an important role for the development and hatching of cocoons. Blackmon (2009) examined whether cocoons would hatch at temperatures ranging from 5 to 30°C. Hatching rate was highest at 10°C and varied between 33, 60, and 100%, depending on the site where earthworms were collected. No hatching occurred at 5°C, and hatching occurred sooner at higher temperatures. Blackmon (2009) also tested whether changes in temperature (e.g., a winter cooling followed by spring warming) would affect hatching. Cocoons were lowered to 5, 10 or 15°C and incubated for 15, 30 or 60 days. Hatching occurred at all incubation lengths, but only at 10ºC, with the exception of one cocoon at 5°C. Cocoons also predominantly hatched 5-6 weeks after warming, regardless of incubation length.

Climate

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ClimateStatusDescriptionRemark
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Dw - Continental climate with dry winter Tolerated Continental climate with dry winter (Warm average temp. > 10°C, coldest month < 0°C, dry winters)
Df - Continental climate, wet all year Preferred Continental climate, wet all year (Warm average temp. > 10°C, coldest month < 0°C, wet all year)

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
31-45

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Bipalium adventitium Predator
Desmognathus monticola Predator
Nephelopsis obscura Predator
Orconectes rusticus Predator
Plethodon metcalfi Predator
Plethodon teyahalee Predator
Scolopocryptops sexspinosus Predator

Notes on Natural Enemies

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The centipede Scolopocryptops sexspinosus and centipedes from the family Cryptopidae, rusty crayfish (Orconectes rusticus), wandering broadhead planarian (Bipalium adventitium), ribbon leech (Nephelopsis obscura) and salamanders Desmognathus monticola, Plethodon metcalfi and P. teyahalee have been documented to prey on A. agrestis (Craft, 2009; Gorsuch and Owen, 2014; Gao et al., 2017).

Means of Movement and Dispersal

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Natural Dispersal
Natural dispersal of A. agrestis can be as fast as 12 m yr-1, but appears to be highly variable and weather dependent (Snyder et al., 2011).

Accidental Introduction
A. agrestis has been - and continues to be - introduced across eastern North America due to two accidental means: the movement of horticultural/landscaping materials (Howell, 1939; Gates, 1958; Tandy, 1969; Bellitürk et al., 2015) and use as fishing bait (Gates, 1958; Callaham et al., 2003). Earth-moving activities, such as road building, may also have introduced the species to new locations, but this has not been formally documented. 

Intentional Introduction
A. agrestis has been intentionally introduced to some environments, in order to start populations of bait near fishing spots (Tandy, 1969). This may have occurred on a broader scale, but it has not been further documented.
 

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Botanical gardens and zoosRaised to feed platypuses Yes Gates, 1954
Escape from confinement or garden escapeMovement with soil or other organic material accompanying plants Yes Gates, 1958
HorticultureMovement with soil or other organic material accompanying plants Yes Yes Gates, 1958; 1966; Tandy, 1969
Hunting, angling, sport or racingIntentional and accidental introduction for bait Yes Yes Gates, 1958; Tandy, 1969; Callaham et al., 2003
Internet salesCan be ordered online Yes Yes Ziemba et al., 2016
Landscape improvementMovement with soil or other organic material accompanying plants Yes Yes Görres and Melnichuk, 2012; Bellitürk et al., 2015
Nursery tradeMovement with soil or other organic material accompanying plants Yes Yes Gates, 1954; 1958; Görres and Melnichuk, 2012

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Mulch, straw, baskets and sodLikely dispersed to many new locations via mulch Yes Yes Bellitürk et al., 2015
Plants or parts of plantsAll stages possible in soil or other organic material accompanying plants Yes Yes Tandy, 1969
Soil, sand and gravelAll stages possible in soil Yes Yes Gates, 1953; 1954; 1958
MailCan be ordered online Yes Yes Ziemba et al., 2016

Environmental Impact

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Impact on Habitats

Snyder et al. (2011) found that, in the Great Smoky Mountains National Park, USA, A. agrestis was effective at removing partially-decomposed litter layers and changing the surface soil structure. Increased presence of A. agrestis was associated with increased amounts of large (> 2 mm) water-stable soil aggregates and a decrease in the thickness of the partially-decomposed (F and H) litter layer. However, A. agrestis presence was not found to change C:N or microbial biomass. Snyder et al. (2013) attributed litter decrease to direct consumption by A. agrestis.

Qiu and Turner (2017) found, both in mesocosms and in the field, decreased amounts of leaf litter due to co-invasion of A. agrestis and A. tokioensis. In mesocosms, surface soils (0-5 cm) showed increased organic matter, total carbon, total nitrogen, C:N and available phosphorus; in the field, these changes occurred, but not at a consistent rate over time. Deeper soils had an increase in inorganic nitrogen and dissolved organic carbon (Qiu and Turner, 2017).

A. agrestis presence also increases activity of lignin-digesting enzymes (Bellitürk et al., 2015).

Impact on Biodiversity

A. agrestis changes the chemistry and physical structure of the litter layer and upper soil, and thus is expected to impact any organisms that use these horizons. Removal of litter, in particular, will affect many detritivorous fauna and litter-dwellers. Snyder et al. (2011; 2013) found that millipede diversity and abundance declined in the field due to A. agrestis invasion, and that there was evidence for direct competition between millipedes (Sigmoria lyrea [Falloria lyrea]) and A. agrestis. Effects on other species are virtually unknown.

Gorsuch and Owen (2014) found that A. agrestis was less likely to be predated than lumbricid earthworms by wandering broadhead planarian (Bipalium adventitium), ribbon leech (Nephelopsis obscura) and seal salamander (Desmognathus monticola). However, this is the only record of A. agrestis from Kentucky and some behaviours described do not fit what is typical for A. agrestis. Given the recent discoveries of multiple Amynthas species living in the same habitat (Chang et al., 2016), it is possible that multiple species were unknowingly used in this experiment.

Several authors have raised concerns about the interaction between A. agrestis and salamanders. Craft (2009) conducted a mesocosm study with salamanders (Plethodon metcalfi and P. teyahalee) using soil from an A. agrestis invasion front. This study showed no difference in salamander body or faeces mass, but the total organic carbon, total nitrogen, and C:N differed significantly, suggesting that prey quantity and/or quality were diminished in the invaded area. A. agrestis was also not a preferred food item in feeding trials.

Ziemba et al. (2015; 2016) found that red-backed salamanders (Plethodon cinereus) and pheretimoid earthworms co-occurred less than expected. Leaf litter layers were qualitatively thinner and lower quality in invaded sites, but there was no effect of invasion on salamander body condition, number of eggs, or tail breakage. In a laboratory study, Ziemba et al. (2015; 2016) also found that P. cinereus used lower quality habitats and consumed less food in the presence of pheretimoid earthworms.

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Abundant in its native range
  • Highly mobile locally
  • Fast growing
  • Reproduces asexually
Impact outcomes
  • Ecosystem change/ habitat alteration
  • Reduced native biodiversity
  • Threat to/ loss of native species
Impact mechanisms
  • Competition
  • Rapid growth
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Difficult to identify/detect as a commodity contaminant
  • Difficult to identify/detect in the field
  • Difficult/costly to control

Uses

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A. agrestis is sometimes used as fishing bait (Gates, 1958; Tandy, 1969; Callaham et al., 2003).

Uses List

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Animal feed, fodder, forage

  • Bait/attractant

General

  • Sport (hunting, shooting, fishing, racing)

Detection and Inspection

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A. agrestis is surface-dwelling and is best found by hand-searching through the leaf litter, at the soil surface, and under logs/rocks (Snyder et al., 2011). Decreased levels of partially-decomposed leaf litter and a granular surface soil may indicate an earthworm invasion, but not necessarily of this species. Wetter areas (e.g., along stream banks, valleys, deeper pockets of leaf litter) and areas impacted by human activity (e.g., roadsides, developed edges of forests) are more likely to support populations of A. agrestis.

Similarities to Other Species/Conditions

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A. agrestis can be easily confused with other pheretimoid earthworms. Amynthas alone includes hundreds of species. Sixteen species in Amynthas and closely related genera have been found in North America; Chang et al. (2016) provide a detailed key for these species. Most species can be easily differentiated from A. agrestis by size, colouration in life, and location of easily observable pores and markings. A. tokioensis and Metaphire hilgendorfi are quite similar to A. agrestis and the three species have been shown to coexist in some locations (Chang et al., 2016). Chang et al. (2016) provide a comparison table to help differentiate these species.

Prevention and Control

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Control

Physical/mechanical control

Blackmon (2009) and Ikeda et al. (2015) examined the role of fire in the control of A. agrestis invasion. Neither study found direct mortality, but both appear to have found indirect impacts: indirect/delayed mortality and weight loss, potentially due to starvation (Blackmon, 2009), and decreased cocoon viability (Ikeda et al., 2015).

Gaps in Knowledge/Research Needs

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Despite its wide dispersal across eastern North America over the last century, the biology and ecology of A. agrestis are very poorly known. The same is true for other invasive pheretimoid species, for which often no information exists beyond their taxonomic description (Burtelow et al., 1998). Understanding traits which aid A. agrestis’ dispersal, establishment and spread (e.g., life history traits, Callaham et al., 2003) is necessary, in order to fully understand and combat these invasions. Tracing pathways of invasion and quantifying their contribution to A. agrestis spread would also be very useful in slowing or stopping the spread of this species.

Earthworm invasions may be nearly impossible to eliminate without wholesale ecosystem destruction, but prescribed fire is one avenue that has shown promise and which needs further exploration.

More research is needed on the diversity of parthenogenetic morphs within the pheretimoids and the distribution of each invading species, as well as effective techniques to accurately identify species.

References

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11/07/17 Original text by:

Bruce A. Snyder, Georgia College & State University, Milledgeville, GA, USA

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