The parasitic worm invader of the New World (Cochliomyia hominivorax) digs its sharp hooks deeper into the United States.
This week, federal and local authorities in Texas confirmed the first known infestation of stampede worms in wildlife since the parasite reappeared in the country this year: a female elk killed by hunters. Although the total number of cases of worm worms is still low, this month has seen an increase.
“We encourage all hunters and landowners to be alert for signs of New World butcherworm when in the field this season,” Alan Cain, director of the wildlife division at the Texas Parks and Wildlife Department, said in a statement released Wednesday.
The return of the butcher worm
The screwworm is actually a species of fly, although its larval form is the real cause for concern. Unlike many species, dung worms love to feed on the living flesh of warm-blooded animals. Flies lay their eggs on a host via open wounds or mucous membranes, then the maggots use their screw-shaped bodies and sharp mouth hooks to burrow deeper into the animal. This can cause significant or even fatal tissue damage in the host, as well as increase the risk of serious secondary infections.
Butcher worm outbreaks have historically devastated livestock populations, but eradication programs in the United States and other countries in the Americas have kept the butcher worm at bay for decades, creating a barrier all the way to Panama. However, recently this barrier has fallen and the parasite has gradually reestablished itself towards the north. In June, the screwworm officially made its return to the United States.
Although maggots can also infect humans, they usually cling to livestock and other animals. This latest case involved an elk captured by hunters in Pecos County, Texas. The elk was found on a game ranch and hunters reported the suspicious case to authorities after harvesting it. The U.S. Department of Agriculture (USDA) Animal and Plant Health Inspection Service confirmed the infestation.
What this means for the United States
As of October 21, according to the USDA, 59 animal cases of New World butcherworm have been detected in Texas and New Mexico, with the most recent being the first found in wildlife. After a lull over the summer, seven new cases were reported this month, the highest number since July.
So far, no human infections have been reported in the country, although such cases have occurred in areas of Mexico where the fly has returned to the United States. Between April 2025 and March 2026, 204 human cases of butcher worms were reported in Mexico, according to a recent report, six of whom subsequently died, including one death directly attributed to the parasite.
In the United States, authorities have implemented containment measures for all cases identified so far, including the latest case. Officials will now modify a previously established infested area, and the Texas Parks and Wildlife Department and USDA plan to conduct additional wildlife monitoring for the New World butcherworm.
It remains possible that these interventions will prevent the parasitic fly from making a full return to the United States. But its new emergence in local wild animals and the recent increase in cases suggest that this situation is still far from under control.
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