Officials have a suspected case of the New World screwworm fly in south Texas, the USDA says
Officials suspect that the New World screwworm fly has arrived in south Texas, the U.S. Department of Agriculture announced Wednesday, marking possibly the first time in decades that it has threatened the nation's cattle industry and only the third time it's appeared in the U.S. in that time.
The USDA said in a post on the social platform X that it was testing a sample from a potential infestation of the fly's flesh-eating larvae at its national veterinary lab in Iowa. The agency did not say exactly where the potential case was identified.
U.S. Agriculture Secretary Brooke Rollins later posted on X that she had met with 50 cattle ranchers and Texas officials, including Gov. Greg Abbott, and said the potential case was “being fully contained.”
“Our food supply is 100% safe,” she said.
Rollins, U.S. and Texas agriculture officials, and cattle industry leaders have been sounding public alarms about the fly's movement across Mexico for more than a year, spurred on by memories of it causing tens of millions of dollars of losses — potentially billions in today’s dollars — before its eradication in the 1970s.
The announcement of the suspected case comes only a day after Rollins had an online news conference to highlight the nearness of the threat, with cases been confirmed in Mexico as close as 25 miles (40 km) from the border — and to outline the USDA's efforts to combat it.
The New World Screwworm fly is a tropical species that decades ago infested cattle in warm weather across the southern United States, but it was contained in Panama until late in 2024. It was eradicated in the U.S. by breeding sterile male flies and releasing them into the wild to mate.
The female fly lays its eggs in open wounds or mucous membranes and they hatch into larvae that eat flesh — making them unlike most fly species — and can infest livestock, wild mammals, household pets and even humans. Infestations can lead to death if left untreated.
In August 2025, federal health officials confirmed a case in a Maryland resident who had traveled to El Salvador, but the victim recovered and officials found no transmission of the parasite. Before that, the last outbreak was in the Florida Keys in September 2016, mostly among wild deer, and it was contained early the next year without spreading further.
The female flies mate once in their monthslong lives, and if they do so with a sterile fly, their eggs would not hatch — and the population would die out over time. Past eradication efforts were so successful that the U.S. shut down facilities for breeding sterile flies, leaving only one in Panama for decades.
That is changing. The USDA dedicated $21 million to convert a fruit-fly breeding facility in southern Mexico into one for breeding screwworm flies, opened a new center for dispersing sterile flies bred elsewhere in southern Texas and has started construction on a $750 million screwworm fly factory there.
Rollins also closed the U.S.-Mexico border last year to livestock imports from Mexico, a decision she defended during her news conference Tuesday. However, she and other USDA officials stressed that pets can cross the border with families, and wild animals on their own.
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