Traps of Rotting Flesh, a Screwworm Defense

The last time the New World screwworm swept through the United States, it devastated livestock and triggered a massive effort to eliminate it. Now UC Riverside researchers are preparing for the parasite’s possible return and planning a preemptive strike before it can regain a foothold.

Despite its name, the screwworm is not a worm at all. It is the flesh-eating larval stage of a shiny blowfly called Cochliomyia hominivorax. Most blowflies are harmless and even useful, but this species feeds on living flesh. “Not all blowflies are this species. We do not have to be afraid of all flies,” said UCR entomologist Amy Murillo.

With funding from the California Department of Food and Agriculture, Murillo and colleague Alec Gerry plan to set traps across the state baited with a lure that smells like rotting flesh. The goal is to spot any sign that the fly, now within 70 miles of the Texas border, is advancing westward. They are also launching an education campaign for veterinarians and livestock handlers, who are most likely to detect early cases.

Murillo encourages vigilance, not panic. For more information, visit https://news.ucr.edu/articles/2025/12/04/preempting-flesh-eating-flys-return-california