A Flesh-Eating Parasite Not Seen in the U.S. for 60 Years Just Turned Up in Texas

A parasite that American agriculture thought it had defeated more than half a century ago has returned. On June 3, 2026, federal officials confirmed the first domestic detection of the New World screwworm in decades — a fly whose larvae burrow into the living flesh of warm-blooded animals, feeding and growing as they go.

The case was identified in a three-week-old calf in Zavala County in South Texas. Larvae were found in the animal's umbilical area, which is a common entry point for screwworm infestation in newborn livestock. The confirmation came from the U.S. Department of Agriculture's Animal and Plant Health Inspection Service, which immediately activated an emergency response in the surrounding area.

What the New World Screwworm Is

The New World screwworm, Cochliomyia hominivorax, is a parasitic fly found primarily in Central and South America. The adult fly resembles an ordinary blowfly, but what it does after mating is not ordinary at all. Females lay eggs on the edges of open wounds — even minor cuts or insect bites — on living animals. When the eggs hatch, the larvae drill downward into the flesh using hooked mouthparts, widening the wound as they feed. Left untreated, a screwworm infestation can kill a large animal within days.

The parasite affects livestock, pets, and wildlife. Human cases are rare but have been documented, typically in people with open wounds who spend extended time outdoors in areas where the fly is active. USDA officials have emphasized that the current threat to human health in the United States is extremely low.