A parasitic fly species known as the New World screwworm (Cochliomyia hominivorax) is rapidly approaching the U.S., raising fears of a return after decades of eradication efforts.
The flesh-eating larvae burrow into wounds of animals and humans, causing severe damage. The U.S. had led a successful campaign since the 1950s by releasing sterilized flies to control the population, eventually establishing a protective barrier at Panama’s Darién Gap.
However, that barrier was breached in 2022. Since then, screwworm cases have surged, advancing 1,600 miles through eight countries to reach Oaxaca and Veracruz, Mexico—just 700 miles from Texas. Rancher Wayne Cockrell warned, “There’s a sense of dread on my part now,” citing undercapacity in sterile fly production.
Efforts to build a new U.S. facility are underway, but experts fear it’s too late to stop the spread. Illegal cattle movement has fueled the parasite’s rapid migration. “The spigot’s still open,” said Jeremy Radachowsky of the Wildlife Conservation Society.
The U.S. suspended cattle imports from Mexico, and lawmakers are pushing new legislation as the livestock industry braces for a potential crisis.