Cochliomyia hominivorax
(New World screwworm)

Pictures

Picture	Title	Caption	Copyright
Title External symptoms Caption Screwworm - Screwworm myiasis in a calf navel. Copyright ©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)	External symptoms	Screwworm - Screwworm myiasis in a calf navel.	©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Title Adult Caption Adult female screwworm fly. Copyright ©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)	Adult	Adult female screwworm fly.	©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)
Title Screwworm larvae Caption Screwworm. Third instar larvae of Cochliomyia hominivorax. Copyright ©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)	Screwworm larvae	Screwworm. Third instar larvae of Cochliomyia hominivorax.	©USDA-2002/Foreign Animal Diseases Training Set/USDA-Animal and Plant Health Inspection Service (APHIS)

Identity

Preferred Scientific Name

• Cochliomyia hominivorax Coquerel

Preferred Common Name

• New World screwworm

Other Scientific Names

• Calliphora hominivorax (COQUEREL)
• Callitroga americana (CUSHING & PATTON)
• Callitroga hominivorax
• Cochliomyia americana
• Lucilia hominivorax

International Common Names

• English: flies, screwworm; Primary screwworm; screw worm; screwworm; screwworms in livestock
• Spanish: Gusano Barrenador del Ganado
• French: lucilie bouchere; ver en vis
• Portuguese: bicheira

Local Common Names

• Aruba: Schroefworm
• Germany: Fliege, Schraubenwurm-
• Netherlands Antilles: Schroefworm

EPPO code

• COCLAM (Cochliomyia americana)
• COCLHO (Cochliomyia hominivorax)

Summary of Invasiveness

Cochliomyia hominivorax (Coquerel) is endemic to the Western Hemisphere, with the exception of Chile., although it has been eradicated from significant parts of its range. Although naturally occurring in relatively low numbers compared with other insect species, C. hominivorax has been introduced and spread into non-endemic and eradicated areas via movement of infested hosts, including humans. Introductions of C. hominivorax, sometimes resulting in outbreaks, have occurred in the United States of America, Mexico, Panama, Curacao, Aruba, Libya, and Australia.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Metazoa
•         Phylum: Arthropoda
•             Subphylum: Uniramia
•                 Class: Insecta
•                     Order: Diptera
•                         Family: Calliphoridae
•                             Genus: Cochliomyia
•                                 Species: Cochliomyia hominivorax

Notes on Taxonomy and Nomenclature

The taxonomy and nomenclature of this species was very confused for over 100 years. Cushing and Patton (1933) documented the difference between Cochliomyia americana C & P and Cochliomyia macellaria Fabricius, which served as a key basis in the eradication of Cochliomyia hominivorax from North America, Central America and parts of the Caribbean. Dear (1985) presents an explanation of the taxonomy and nomenclature of C. hominivorax and other members of the Chrysomyini.

Distribution

Cochliomyia hominivorax is endemic to the Western Hemisphere and occurs in tropical, subtropical, and temperate zones. Northern and southern limits of its range are primarily due to cold weather. Cochliomyia hominivorax is present in all South American countries with the exception of Chile. This species is also present in Cuba, the Dominican Republic, Haiti, Jamaica, and Trinidad and Tobago. Cochliomyia hominivorax has been eradicated from the United States of America, Mexico, Guatemala, Belize, Honduras, El Salvador, Nicaragua, Costa Rica, and Panama (an outbreak in Florida in 2016 was eradicated in 2017). A barrier zone is maintained in Panama using sterile flies and field operations to prevent immigration of C. hominivorax into eradicated areas. Eradication has also been achieved in Curacao, Netherlands Antilles, British Virgin Islands, US Virgin Islands, and Puerto Rico.

Distribution Table

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.

Introductions

Risk of Introduction

Risk of introduction of C. hominivorax may be relatively low; however, movement of infested hosts into non-infested habitats remains a risk. As long as populations of C. hominivorax exist in the Western Hemisphere, modern travel conveyances, especially aircraft, make the introduction of C. hominivorax continents away from the original source of infestation a real possibility. Adults of C. hominivorax can occasionally enter cars, boats, ships, and aircraft, but this is extremely rare.

Pathogen Characteristics

Detailed descriptions of the life stages of C. hominivorax are presented in Laake et al. (1936).

Eggs: Eggs are bright white, approximately 1.04 mm long and 0.26 mm in diameter with a cylindrical shape, rounded at the posterior end and flattened at the anterior end with a dorsal seam extending from the anterior end almost to the posterior end of the egg. Eggs are laid in a parallel pattern in layers glued together to form a mass which gives them the appearance of a shingled roof. Eggs are laid in masses which contain from 10 to 400. Eggs are generally laid on or near the edges of wounds but may also be laid on or near host body orifices with purulent discharge. Eggs have also been observed laid approximately 5 cm from the edge of wounds under the moist wool of sheep in Costa Rica during the rainy season (J Welch, personal observation).

Larvae: First instar larvae are approximately 1.2 mm and 0.23 mm, length and diameter, respectively, at hatching and are clear with internal structures visible. Mature first instar larvae are approximately 3.6 mm and 0.57 mm, length and diameter, respectively, and are whitish in colour. Newly molted second instar larvae are generally whitish in colour and are approximately 3.5mm and 0.6mm, length and diameter, respectively. Mature second instar larvae are approximately 6.3 mm to 7.4 mm and 1.5 mm, length and diameter, respectively, and are whitish to cream coloured. Third instar larvae are white to cream to pink coloured depending on diet, and are approximately 6.4 mm to 17 mm in length and 1.6 mm to 3.5 mm in diameter. All larval instars have characteristic bands of spines on most segments and a pair of heavily sclerotized mouth hooks, main tracheal trunks and spiracles. The spiracles with three slit-like openings are almost completely surrounded by heavily sclerotized peritremes, but which appear incomplete ventrally.

Pupae: Pupae are barrel-shaped and dark brown in colour. They are approximately 10.2 mm and 4.3 mm in length and width, respectively.

Adults:Laake (1936) reported that flies are generally deep metallic greenish-blue in colour. Colour is variable, ranging from metallic light to dark green, light grayish-blue through sky-blue to dark blue (J Welch, personal observation). Flies have three dark longitudinal stripes on the dorsal part of the thorax. C. hominivorax adults are approximately 2-3 times the size of a house fly.

List of Symptoms/Signs

Climate

Latitude/Altitude Ranges

Air Temperature

Rainfall

Natural enemies

Notes on Natural Enemies

Cochliomyia hominivorax occurs in relatively low numbers compared with other insect species. Populations are aggregated yet mobile within favourable habitats. As a result, no natural enemies specific for C. hominivorax have been identified. Other insects, birds, frogs, lizards and spiders feed on adult C. hominivorax.Welch (1993) describes the predation of ground-released sterile C. hominivorax flies by spiders. Ants (especially Solenopsis sp.) are common predators of larvae that have exited wounds to pupate and have been observed pulling larvae from wounds (J Welch, unpublished data). There are no data to suggest that natural enemies are important to the population dynamics of C. hominivorax.

Economic Impact

Myiasis by C. hominivorax results in a negative economic impact by a decrease in animal weights and milk production, and an increase in animal death. Additionally increase in the costs of inspection and handling of animals, and the increase in costs of insecticides, and veterinary services and medicines results in a negative economic impact (Wyss, 2000). Wyss (2000) reported substantial annual economic benefits to producers (US$ with conversion to 2015 US$ in parentheses) after eradication of C. hominivorax; $896.1 million ($1.25 billion) for the United States of America, $328.6 ($458.5) million for Mexico, and $87.8 ($122.5) million for all of the Central America countries combined. Expanding the analysis of the economic impact of eradicating C. hominivorax from Central America by adding linkages to the economy and consumer benefits resulted in an estimated total annual economic impact of $704.3 ($982.6) million to consumers (Wyss, 2000). Wyss (2002) estimated the annual economic benefits to producers in South America as $2.8 ($3.91) billion.

Environmental Impact

Impact on habitats is none or unknown.

Impact on biodiversity is low, but may become more important in localized areas during conditions which promote the increase of C. hominivorax populations. Fuller (1962) reported that mortality of fawns of White-tailed deer, Odocoileus virginianus (Zimmerman), ranged from 20 to 80 percent annually depending on environmental and population conditions.

Social Impact

Infestation of humans is under-reported due to the negative social implications. Those humans who cannot take care of themselves are especially vulnerable. Although the young, old, and mentally challenged are more susceptible to myiasis, all humans are potential hosts. Humans living in areas of favorable habitats for C. hominivorax are at a higher risk than those living in unfavorable habitats.

Risk and Impact Factors

• Invasive in its native range
• Proved invasive outside its native range
• Has a broad native range
• Abundant in its native range
• Pioneering in disturbed areas
• Tolerant of shade
• Capable of securing and ingesting a wide range of food
• Highly mobile locally
• Benefits from human association (i.e. it is a human commensal)
• Fast growing
• Has high reproductive potential

• Damaged ecosystem services
• Ecosystem change/ habitat alteration
• Host damage
• Increases vulnerability to invasions
• Negatively impacts agriculture
• Negatively impacts cultural/traditional practices
• Negatively impacts human health
• Negatively impacts animal health
• Negatively impacts livelihoods
• Reduced amenity values
• Reduced native biodiversity
• Threat to/ loss of endangered species
• Threat to/ loss of native species
• Damages animal/plant products
• Negatively impacts trade/international relations

• Parasitism (incl. parasitoid)
• Pathogenic
• Rapid growth

• Difficult to identify/detect as a commodity contaminant
• Difficult to identify/detect in the field
• Difficult/costly to control

Gaps in Knowledge/Research Needs

Research is needed on:

1.     Population dynamics and distribution of C. hominivorax in the Amazon Basin.

2.     Development of an attractant for male C. hominivorax.

3.     Development of a new wound-treatment as coumaphos is no longer being produced.

References

Baumhover AH, 1963. Susceptibility of screwworm larvae and prepupae to dessication. Journal of Economic Entomology, 56:473-475.

Baumhover AH, 1997. A personal account of programs to eradicate the screwworm, Cochliomyia hominivorax, in the United States and Mexico with special emphasis on the Florida program. Pioneer lecture presentation by the Florida Entomological Society, Daytona Beach, Florida, 4 August 1997. 52 pp.

Coquerel C, 1858. Des larves de diptéres developpés dans le sinus frontause et les fossess nasals de l'homme á Cayenne. Archives Genérales Médecines, 5:513-528.

Coronado A, Kowalski A, 2009. Current status of the New World screwworm Cochliomyia hominivorax in Venezuela. Medical and Veterinary Entomology, 23(s1):106-110. http://www.blackwell-synergy.com/loi/mve

Cushing EC, Patton WS, 1933, 20th December. Studies on the Higher Diptera of 134 Medical and Veterinary Importance. Cochliomyia americana sp. nov., the Screw-worm Fly of the New World. Ann. Trop. Med. Parasit, 27(4):539-551 pp.

Dear JP, 1985. A revision of the New World Chrysomyini (Diptera: Calliphoridae). Revista Brasileira de Zoologia, 3(3):109-169.

FAO, 1992. The new world screwworm eradication programme North Africa 1988-1992. Rome, Italy: FAO, 192 pp.

Forero B E, Cortés V J, Villamil J L, 2008. The problem of screwworm, Cochliomyia hominivorax (Coquerel, 1858), in Colombia. (Problemática del gusano barrenador del Ganado, Cochliomyia hominivorax (Coquerel, 1858) en Colombia.) Revista MVZ Cordoba, 13(2):1400-1414. http://apps.unicordoba.edu.co/revistas/revistamvz/mvz-132/v13n2a16.pdf

Fuller G, 1962. How screwworm eradication will affect wildlife. The Cattleman, 48:82-84.

Grant GH, Snow JW, Teran MV, 2000. The New World screw-worm as a pest in the Caribbean and plans for its eradication from Jamaica and the other infested Caribbean islands. In: Area-wide control of fruit flies and other insect pests. Joint proceedings of the international conference on area-wide control of insect pests, 28 May-2 June, 1998 and the Fifth International Symposium on Fruit Flies of Economic Importance, Penang, Malaysia, 1-5 June, 1998 [ed. by Tan, K. -H.]. Pulau Pinang, Malaysia: Penerbit Universiti Sains Malaysia, 87-93.

Krafsur ES, Whitten CJ, Novy JE, 1987. Screwworm eradication in North and Central America. Parasitology Today, 3(5):131-137.

Laake EW, 1950. Screw-worm Survey in western United States, 1949. Journal of Economic Entomology, 43(3):387-389 pp.

Laake EW, Cushing EC, Parish HE, 1936. Biology of the Primary Screw Worm Fly, Cochliomyia americana, and a Comparison of its Stages with those of C. macellaria. Technical Bulletin. United States Department of Agriculture, 500. 24 pp.

Mangan RL, Thomas DB, 1989. Habitat preferences and dispersal patterns in native female screwworm flies (Diptera: Calliphoridae). Annals of the Entomological Society of America, 82(3):332-339.

OIE Handistatus, 2002. World Animal Health Publication and Handistatus II (dataset for 2001). Paris, France: Office International des Epizooties.

OIE Handistatus, 2003. World Animal Health Publication and Handistatus II (dataset for 2002). Paris, France: Office International des Epizooties.

OIE Handistatus, 2004. World Animal Health Publication and Handistatus II (data set for 2003). Paris, France: Office International des Epizooties.

OIE Handistatus, 2005. World Animal Health Publication and Handistatus II (data set for 2004). Paris, France: Office International des Epizooties.

OIE, 2009. World Animal Health Information Database - Version: 1.4. World Animal Health Information Database. Paris, France: World Organisation for Animal Health. http://www.oie.int

Osorio J, Moncada L, Molano A, Valderrama S, Gualtero S, Franco-Paredes C, 2006. Role of ivermectin in the treatment of severe orbital myiasis due to Cochliomyia hominivorax. Clinical Infectious Diseases, 43(6):e57-e59. http://www.journals.uchicago.edu/CID/journal/home.html

Parker FD, Welch JB, 1992. Monitoring adult populations of the screwworm (Diptera: Calliphoridae) with feeding stations baited with liver. Journal of Economic Entomology, 85(5):1740-1753.

Parker FD, Welch JB, Matlock RB, 1993. Influence of habitat, season, and attractant on adult behavior of the screwworm (Diptera: Calliphoridae) in a tropical dry zone in Costa Rica. Journal of Economic Entomology, 86(5):1359-1375.

Parman DC, 1945. Effect of Weather on Cochliomyia americana and a Review of Methods and economic Applications of the Study. 66-76 pp.

Phillips PL, Welch JB, Kramer M, 2004. Seasonal and spatial distributions of adult screwworms (Diptera: Calliphoridae) in the Panama canal area, Republic of Panama. Journal of Medical Entomology, 41(1):121-129.

Skoda, S. R., Phillips, P. L., Welch, J. B., 2018. Screwworm (Diptera: Calliphoridae) in the United States: Response to and Elimination of the 2016–2017 Outbreak in Florida, Journal of Medical Entomology, 55 https://doi.org/10.1093/jme/tjy049

Thomas DB, Mangan RL, 1989. Oviposition and wound-visiting behavior of the screwworm fly, Cochliomyia hominivorax (Diptera: Calliphoridae). Annals of the Entomological Society of America, 82(4):526-534.

Welch JB, 1993. Predation by spiders on ground-released screwworm flies, Cochliomyia hominivorax (Diptera: Calliphoridae) in a mountainous area of southern Mexico. Journal of Arachnology, 21(1):23-28.

Williams DL, Gartman SC, Hourrigan L, 1977. Screwworm eradication in Puerto Rico and the Virgin Islands. World Animal Review, No. 21:31-35.

Wyss JH, 2000. Screw-worm eradication in the Americas - overview. In: Area-wide control of fruit flies and other insect pests. Joint proceedings of the international conference on area-wide control of insect pests, 28 May-2 June, 1998 and the Fifth International Symposium on Fruit Flies of Economic Importance, Penang, Malaysia, 1-5 June, 1998 [ed. by Tan, K. -H.]. Pulau Pinang, Malaysia: Penerbit Universiti Sains Malaysia, 79-86.

Wyss JH, 2002. Overview of the sterile insect technique in screw-worm fly eradication. In: Proceedings of the screw-worm fly emergency preparedness conference, Canberra, Australia, 12-15 November 2001. Canberra, Australia: Agriculture, Fisheries, and Forestry, 176-181.

Links to Websites

Organizations

World: OIE (World Organisation for Animal Health), 12, rue de Prony, 75017 Paris, France, http://www.oie.int/

Panama: COPEG (Panama-United States Commission for the Eradication and Prevention of Screwworm), http://www.copeg.org/

Austria: IAEA (International Atomic Energy Agency), Vienna International Centre, PO Box 100, A-1400 Vienna, http://www.iaea.org/

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

USA: USDA-APHIS (Animal and Plant Health Inspection Service), US Department of Agriculture 1400, Independence Ave., SW Washington, DC 20250, Washington, DC, USA, http://www.aphis.usda.gov/

Contributors

27/01/16 Original text by:

John B. Welch, USDA-APHIS-IS, USDA-ARS-SPARC, 2881 F&B Road, College Station, Texas, USA

Distribution Maps