The flesh-eating New World screwworm has been confirmed in a Texas calf, marking the first detection of the parasite in U.S. livestock in decades.
The Department of Agriculture announced Wednesday that a three-week-old calf in Zavala County, Texas, tested positive for New World screwworm — a parasite whose larvae feed on the living tissues of warm-blooded animals.
The screwworm infestation was found in the calf’s umbilical area.
The parasite typically enters animals through open wounds, where larvae burrow into the flesh and feed on living tissue. Federal officials said no additional cases have been identified in the United States.
“All models showed New World screwworm entering the country in 2025; however, thanks to the hard work across the entire Trump administration and our industry, state, and local partners, we were able to buy time for this moment.”
Dudley Hoskins, Under Secretary for Marketing and Regulatory Programs, said protecting America’s livestock is a national security issue of the utmost importance.
Hoskins added: “USDA invested heavily in the tools needed to eliminate NWS ever since cases started increasing in Central America and Mexico. The United States has defeated this pest before, and we will do it again.”
🚨 With the recent detection of New World screwworm in a 3-week-old bovine in Zavala County, TX, USDA urges residents to contact your veterinarian right away if you see any suspicious wounds, maggots, or infestations in your animals or herd.
If you see signs of maggot… pic.twitter.com/lxxsjIgDcb
— Dept. of Agriculture (@USDA) June 4, 2026
The U.S. case comes after the screwworm was found last week in a five-year-old goat in Coahuila, the Mexican state that borders southwestern Texas. A separate case was reported Sunday — the screwworm infecting a dog in Tamaulipas, another bordering Mexican state.
The current outbreak in Mexico has persisted for some time, prompting Secretary of Agriculture Brooke Rollins to shut down livestock trade across the southern border in May 2025.
There was one confirmed U.S. case last year from a person who returned to Maryland after traveling to El Salvador.
The USDA reports that screwworm maggots cause painful, foul-smelling wounds — and that maggots can sometimes be seen or felt in open wounds or in body openings, including the nose, mouth, eyes, ears, and genitals.
If the infestation isn’t caught early and treated quickly, it can lead to extensive tissue damage and sometimes death.
Adult screwworm flies are the size of a housefly, with orange eyes, a metallic blue or green body, and three dark stripes along their backs. The parasite is typically found in South America and parts of the Caribbean, but has been found farther north over the last three years.
If mammals or birds are found showing signs of irritated behavior, head shaking, a decaying odor, or maggots in wounds, they should be reported to an animal health official immediately.
The USDA warns that anyone who sees signs of maggot infestations in live or very recently dead wild animals, especially in areas near the U.S.-Mexico border, should call 866-487-3297 or report it to their local USDA Wildlife Services office.
