It’s the stuff nightmares are made of. A fly lands on an open wound and lays hundreds of eggs, from which hatch countless ravenous maggots. There they writhe, devouring flesh, insatiable and relentless. Every minute they dig deeper and deeper until flesh gives way to bone. Even the species name of these maggots inspires a shiver of fear: Cochliomyia hominivorax – “man eater”. This nightmare of a fly is the horrifying reality for many mammals in South America and some Caribbean islands, particularly cattle. And it seems to be making a comeback in the places it was previously eradicated – Central and North America. What exactly this fly does, why it’s such a problem, and how we came to defeat it (temporarily) all feature in this week’s episode. Sterile flies? Archival footage? Gnarly descriptions? This episode has it all.
| History | Biology |
| Silent Spring. Carson Rachel . 368 pp. illus., Houghton Mifflin Company, Boston. (1962) | Thomas, D.B. and Mangan, R.L., 1989. Oviposition and wound-visiting behavior of the screwworm fly, Cochliomyia hominivorax (Diptera: Calliphoridae). Annals of the Entomological Society of America, 82(4), pp.526-534. |
| Gillman, Helen. The New World Screwworm Eradication Programme: North Africa, 1988-1992. Food & Agriculture Org., 1992. | Wyss, J.H., 2000. Screwworm eradication in the Americas. Annals of the new York Academy of Sciences, 916(1), pp.186-193. |
| Graham, F. (1984). The Dragon Hunters. United States: E.P. Dutton. | Scott, M.J., Concha, C., Welch, J.B., Phillips, P.L. and Skoda, S.R., 2017. Review of research advances in the screwworm eradication program over the past 25 years. Entomologia Experimentalis et Applicata, 164(3), pp.226-236. |
| Alexander, James L. “Screwworms.” Journal of the American Veterinary Medical Association 228.3 (2006): 357-367. | USDA: New World Screwworm Story Map March 2017. https://www.aphis.usda.gov/livestock-poultry-disease/cattle/new-world-screwworm-mapping |
| Aubertin, D., and P. A. Buxton. “Cochliomyia and myiasis in tropical America.” Annals of Tropical Medicine & Parasitology 28.3 (1934): 245-254. | Alexander, J.L., 2006. Screwworms. Journal of the American Veterinary Medical Association, 228(3), pp.357-367. |
| Coquerel, Ch. “Note sur les larves appartenant à une espèce nouvelle de diptère (Lucilia hominivorax) developpées dans les sinus frontaux de l’homme à Cayenne.” Annales de la Société entomologique de France. Vol. 3. 1858. | Thomas, D.B., 1993. Behavioral aspects of screwworm ecology. Journal of the Kansas Entomological Society, pp.13-30. |
| e Souza, Kelly da Silva, et al. “Demographic and historical processes influencing Cochliomyia hominivorax (Diptera: Calliphoridae) population structure across South America.” Parasites & Vectors 18.1 (2025): 18. | Valdez-Espinoza, U.M., Fadda, L.A., Marques, R., Osorio-Olvera, L., Jiménez-García, D. and Lira-Noriega, A., 2025. The reemergence of the New World screwworm and its potential distribution in North America. Scientific Reports, 15(1), p.23819. |
| Fresia, Pablo, Ana Maria L. Azeredo-Espin, and Mariana L. Lyra. “The phylogeographic history of the New World screwworm fly, inferred by approximate Bayesian computation analysis.” PLoS One 8.10 (2013): e76168. | Hickner, P.V., Mittapalli, O., Subramoniam, A., Sagel, A., Watson, W., Scott, M.J., Arp, A.P., de León, A.A.P. and Syed, Z., 2020. Physiological and molecular correlates of the screwworm fly attraction to wound and animal odors. Scientific Reports, 10(1), p.20771. |
| Gutierrez, A. P., L. Ponti, and P. A. Arias. “Deconstructing the eradication of new world screwworm in North America: retrospective analysis and climate warming effects.” Medical and veterinary entomology 33.2 (2019): 282-295. | de Barros, G.P. and Bricarello, P.A., 2020. Myiasis by Cochliomyia hominivorax (Coquerel, 1858): a neglected zoonosis in Brazil. Open Journal of Veterinary Medicine, 10(6), pp.80-91. |
| Hall, M. J. R. “Screwworm flies as agents of wound myiasis.” World animal review 1991 (1991): 8-17. | WOAH. Aug 22, 2025. New World screwworm continues to spread: WOAH calls for strong collaboration across livestock sectors and borders. https://www.woah.org/en/new-world-screwworm-continues-to-spread-woah-calls-for-strong-collaboration-across-livestock-sectors-and-borders/ |
| Klassen, W., et CF Curtis, and J. Hendrichs. “History of the sterile insect technique.” Sterile insect technique. CRC Press, 2021. 1-44. | Treisman, R. Aug 25, 2025. The US confirms its first human case of New World Screwworm. What is it? NPR, All things considered. https://www.npr.org/2025/08/25/nx-s1-5515487/new-world-screwworm-us-human-case |
| Knipling, Edward F. “The eradication of the screw-worm fly.” Scientific American 203.4 (1960): 54-61. | APHIS Sept 2,2025. New World Screwworm outbreak in Central America and Mexico. https://www.aphis.usda.gov/livestock-poultry-disease/cattle/ticks/screwworm/outbreak-central-america |
| Lindquist, D. A., M. Abusowa, and M. J. R. Hall. “The New World screwworm fly in Libya: a review of its introduction and eradication.” Medical and veterinary entomology 6.1 (1992): 2-8. | USDA June 18,2025. New World Screwworm Domestic Readiness and Response Policy Initiative. https://www.usda.gov/sites/default/files/documents/nws-visit-policy-brief.pdf |
| Nasser, Mohamed G., et al. “Evolutionary profile of the family Calliphoridae, with notes on the origin of myiasis.” Saudi Journal of Biological Sciences 28.4 (2021): 2056-2066. | |
| Spradbery, J. P. “Screw-worm fly: a tale of two species.” Agricultural Zoology Reviews 6.1 (1994). | |
| Stevens, Jamie R., and James F. Wallman. “The evolution of myiasis in humans and other animals in the Old and New Worlds (part I): phylogenetic analyses.” TRENDS in Parasitology 22.3 (2006): 129-136. | |
| Stevens, Jamie R., et al. “The evolution of myiasis in humans and other animals in the Old and New Worlds (part II): biological and life-history studies.” TRENDS in Parasitology 22.4 (2006): 181-188. | |
| Valdez-Espinoza, Uriel Mauricio, et al. “The reemergence of the New World screwworm and its potential distribution in North America.” Scientific Reports 15.1 (2025): 23819. | |
| Van der Vloedt, A. M., and W. Klassen. “The development and application of the sterile insect technique (SIT) for New World screwworm eradication.” World Animal Review (1991): 42-49. | |
| Vargas-Terán, Moisés. “The new world screwworm in Mexico and Central America.” (1991): 28-35. | |
| Welch, John B. “A detector dog for screwworms (Diptera: Calliphoridae).” Journal of economic entomology 83.5 (1990): 1932-1934. | |
| STOP Screwworms: Selections from the Screwworm Eradication Collection, National Agricultural Library, USDA. | |
| Severn Run’s Cazador (Caz), Screwworm Detection Dog, Collection: Screwworm Eradication Program Records | |
| Screwworm Eradication Program Records: Oral Histories. National Agricultural Library. Uploaded to Internet Archive. | |
| Who Shall Reap? Film by US Department of Agriculture. 1969. Uploaded to Internet Archive. | |
| Firsthand account video: United States Department of Agriculture. 1963. “Look Out for Screwworms.” Special Collections, USDA National Agricultural Library. Accessed August 28, 2025, https://www.nal.usda.gov/exhibits/speccoll/items/show/6900. |
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