The U.S. Department of Agriculture on Wednesday confirmed the country’s first case of New World screwworm — the parasitic fly poised to harm the state’s $15 billion cattle industry — in South Texas.
The USDA tested a sample from La Pryor in Zavala County at the USDA’s National Veterinary Services Laboratories in Ames, lowa, confirming the infestation, Secretary Brooke Rollins said during a press conference about the case. The infested animal is a three-week old calf, and there have been no other detections so far.
The USDA said in a social media post earlier Wednesday that it was testing a suspected screwworm sample and that it had already activated personnel on the ground and were working with local partners.
The confirmation comes one day after Rollins debunked the claims of a state lawmaker that the screwworm was less than 1 mile from the U.S.-Mexico border.
State and federal officials had been bracing for the arrival of screwworm for months, fearing its potential impact to livestock and the agriculture industry at-large.
The parasitic fly targets the live flesh of warm mammals including cattle, pets, wildlife and humans. Screwworm infects them by embedding their larvae in open wounds. The larvae feed off the flesh, causing severe wounds or death.
Rollins said residents near affected areas should check their pets for signs of screwworm infection, which include infected wounds and screwworm eggs or larvae. She also said that issues with screwworms should not cause food supply chain issues, as screwworms do not infest meat, fruits or vegetables.
Screwworm had been eradicated in the U.S. since the 1960s when the pest was pushed back into Central America. However, cases began springing up in Panama, Costa Rica, Nicaragua, and Honduras. In 2024, Mexico reported its first case.
Since early 2025, the U.S. has deployed more than 8,000 traps capable of detecting screwworm, Rollins said, resulting in 58,000 samples and 19,000 wildlife tested — all of which tested negative, until today’s case.
Rollins blamed the spread of screwworm toward the U.S.-Mexico border on “the open-border policies of the last administration and the resulting illicit cattle movement” in a separate social media post an hour before Wednesday’s press conference. She also said that she met virtually with Texas’ Animal Health Commission and about 50 cattle ranchers, and has been in contact with Gov Greg Abbott and Texas House Speaker Dustin Burrows.
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On Monday, state Rep. Don McLaughlin, a Uvalde Republican, claimed the fly was just one mile away from Texas. Rollins dismissed those claims Tuesday at a news conference, calling McLaughlin “well-intentioned” but wrong.
“Well … maybe we should listen to our state representatives,” McLaughlin tweeted after the USDA announced the suspected case Wednesday.
We’ve already established that Brooke Rollins is an unqualified hack, but we always appreciate another illustration of it. Even Sid Miller is critical of the USDA’s response to the screwworm threat. This background story on the New World screwworm adds a bit of context.
The spread of New World screwworms across Central America has been very rapid, seemingly traveling hundreds of miles within weeks.
Animal experts believe the movement is too quick to be done by the fly itself, meaning people were clearly shipping infested livestock around Central America.
Screwworms usually don’t stray too far from their natural tropical and subtropical climates on their own. The parasitic flies do not tolerate prolonged periods of very dry, hot, or very cold weather. Rapid spread in a country is mainly due to humans moving infested animals over large distances.
After Mexican officials confirmed a case of screwworm in November 2024, the USDA, under former President Joe Biden, closed southern ports of entry to live cattle imports to prevent the spread of screwworm into the U.S. However, the move also strained the supply of cattle in the state, hitting some in the cattle industry hard.
The USDA reversed course in February 2025, after President Donald Trump took office, announcing the opening of the ports, only to close them again in May 2025.
In an effort to prevent its spread, the USDA shut down the southern border to live animal imports in May 2025, preventing cattle from Mexico from entering the U.S. and limiting the supply of cattle in Texas.
It’s currently unknown how the screwworm infestation reached South Texas.
Now we get to try to make it go away again. The “sterile fly” technique, which was used before with success, will be used again. Today I Learned that the facility that generates these sterile flies, which is in Panama, had its production disturbed by the COVID pandemic. Who knew? More from the Trib here, and NBC News and the Associated Press have more.
UPDATE: And now there’s two.