Cochliomyia hominivorax

(Coquerel, 1858)

New World screwworm fly, New World screwworm, screwworm, screw-worm

Cochliomyia hominivorax, the New World , is an obligate parasitic blowfly whose feed exclusively on living tissue of vertebrates. It is the only parasitic in its ; other Cochliomyia species are facultative or carrion feeders. The species was eradicated from the United States, Central America, and much of the Caribbean through the technique beginning in the 1950s, though it persists in tropical and subtropical South America and portions of the Caribbean. A 2016 in the Florida was successfully eliminated, but in southern Mexico in 2024–2025 triggered renewed efforts and trade restrictions.

SterileMaleCochliomyiahominivorax by Peggy Greb. Used under a Public domain license.

Cochliomyia hominivorax (Coquerel, 1858) by The Mexican-American Commission for the Eradication of the Screwworm. Used under a Public domain license.

Cochliomyia hominivorax by Astridlorena. Used under a CC BY 3.0 license.

Pronunciation

How to pronounce Cochliomyia hominivorax: //ˌkɒk.li.oʊˈmaɪ.ə ˌhɒm.ɪˈnɪv.əˌræks//

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

resemble other metallic blowflies but are distinguished by thoracic striping pattern and association with living . are definitively identified by examining : C. hominivorax has a complete with a distinct button, and the spiracular slits are straight or slightly sinuous. This contrasts with Cochliomyia macellaria (secondary ), which has an incomplete peritreme and more sinuous slits, and feeds on necrotic tissue rather than living flesh. Genetic identification via COI sequencing is standard for confirmation in programs.

Images

Habitat

Tropical and subtropical environments where vertebrate are present. Requires temperatures above 10°C for sustained activity; collapse in winter in marginal areas. Associated with agricultural landscapes, rangelands, and natural areas supporting mammal populations. Cannot persist without access to living hosts, as are obligate .

Distribution

Currently to tropical and subtropical South America, including Brazil, Uruguay, Paraguay, Bolivia, Peru, Colombia, Venezuela, and the Guianas; also present in parts of the Caribbean including Cuba, Jamaica, Hispaniola, and Trinidad. Eradicated from the United States (1966, with isolated 2016 Florida ), Mexico (previously, though re-detected 2024–2025), Central America to the Panama Canal zone, and most Caribbean islands. A permanent sterile barrier is maintained in eastern Panama to prevent northward spread.

Seasonality

Year-round activity in tropical core range with continuous breeding. In subtropical marginal areas, activity peaks during warm months; decline or disappear in winter. In southern Argentina, cease during winter and early spring. time is approximately 20 days under favorable conditions.

Diet

feed exclusively on living and subdermal tissues of vertebrates. Cannot develop in carrion or on animals. feed on nectar, , and other sugar sources; do not feed on blood or .

Host Associations

Bos taurus - larval major economic ; cattle industry losses historically severe
Ovis aries - larval sheep and goats susceptible
Sus scrofa - larval domestic and swine
Equus caballus - larval horses and other equids
Canis lupus familiaris - larval domestic dogs
Felis catus - larval domestic cats
Odocoileus virginianus - larval -tailed deer; 80% fawn mortality reported in Texas historically
Pteronura brasiliensis - larval giant otter; first documented case 2022, Pantanal, Brazil
Panthera onca - larval jaguar; documented in endangered
Homo sapiens - larval human documented but less frequent than livestock

Life Cycle

Females 250–500 in exposed wounds or body orifices of ; can lay up to 3,000 eggs in lifetime. Eggs hatch in 12–24 hours. burrow into living tissue, feeding and growing through three over 3–7 days. Third instar larvae exit wound and drop to ground to pupate in soil. Pupal stage lasts approximately 7 days. emerge, mate on vegetation, and females seek hosts within 4–5 days. Total time approximately 20 days at optimal temperatures. Females mate once and store sperm for life; males mate up to 10 times.

Behavior

Females are attracted to wounds by olfactory cues including and carbon dioxide. They exhibit strong capacity, dispersing 80–160 km per ; individual females can up to 200 km in lifetime. Males are relatively sedentary, hiding in vegetation until detecting females via visual and chemical cues. exhibit negative , burrowing deeper into tissue when disturbed— that gives the its . means larvae cannot survive in necrotic tissue or carrion, distinguishing this species from facultative .

Ecological Role

are driven entirely by availability; no significant role as or in due to inability to use carrion. In areas, acts as control on wild mammals, particularly and individuals with wounds. Absence of effective at ; fire and other may take some but do not regulate populations. programs have eliminated the from most of its former range, demonstrating that function is not dependent on this .

Human Relevance

One of the most economically significant livestock pests in . Prior to , cost U.S. cattle industry hundreds of millions of dollars annually; current prevention saves estimated $1.3 billion yearly. Eradication via technique (SIT) pioneered on this , now applied globally to , , and mosquitoes. Trade restrictions and animal are required to prevent reintroduction. Human occurs but is rare; cases require surgical removal of and wound treatment. 2016 Florida threatened endangered Key deer; 2024–2025 Mexico triggered emergency USDA response and livestock import bans.

Similar Taxa

Cochliomyia macellariaSecondary ; feed on necrotic tissue and carrion, not living flesh. Distinguished by larval (incomplete ) and facultative rather than . Often found in wounds already infested with C. hominivorax.
Chrysomya bezzianaOld World ; convergent ecological role but different , geographically separated. Occurs in Africa, Asia, and Papua New Guinea. Morphologically similar but not present in the Americas.
Lucilia sericataCommon green bottle ; metallic green blowfly that may cause in wounds but primarily breeds on carrion. do not attack healthy tissue.

More Details

Etymology

name from Greek kochlias ( with spiral shell) + myia (); epithet from Latin hominis (man) + vorax (consuming), reflecting human potential. Formerly placed in genus Callitroga (Greek kallos, beautiful + trogein, to gnaw) as C. americana.

Sterile Insect Technique

First on which SIT was developed and deployed. Mass-reared males are sterilized by ionizing radiation and released to mate with wild females, producing no offspring. COPEG facility in Panama produces ~20 million sterile weekly for barrier maintenance and response. Technique requires females to mate only once, which C. hominivorax does naturally.

Mass Rearing Diet

in production facilities are reared on formulated diets containing dried bovine blood components. Current COPEG uses 8:2 hemoglobin-to-plasma ratio, replacing earlier whole blood preparations that became unavailable commercially.