McALLEN — 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.
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.
U.S. officials are also working with officials in Mexico and Panama to try to eradicate the screwworm again using the sterile fly method. This practice consists of producing male sterile flies to have them reproduce unviable eggs with female flies who can only reproduce once in their lifetime.
At the time of their spread from Central America into Mexico, there was only one sterile fly production facility, located in Panama. Since then, U.S. officials have helped launch another in Metapa, Mexico and are building another in Edinburg, Texas, which Rollins said is slated to open in fall 2027.
They’ve also launched two fly dispersal facilities, which help distribute sterile flies in needed areas, in Tampico, Mexico and Edinburg.
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.
“If this case is confirmed I will stand lockstep with every local, state and federal agency to work together and fight this horror,” he said. “As we gather more information and work with different agencies we will keep South Texas informed and protected.”
Texas Agriculture Sid Miller criticized the federal government’s response to screwworm as “slow, bureaucratic, and [an] incomplete response” in a press release on Wednesday shortly before the case was confirmed. He also asked President Donald Trump to approve deployment of the Screwworm Adult Suppression System, which was tested by the U.S. in the late 1970s to eradicate screwworms using bait and insecticides.
In an interview with The Texas Tribune on Tuesday before the Texas screwworm case was confirmed, Miller said he was frustrated with the current response and that the SWASS system could quickly solve a potential outbreak.
“It’s the most frustrating thing I’ve run up against in my 12 years as Ag Commissioner,” Miller said. “We have the ability to shut that and eradicate that screwworm. We can do it in about 60 days. USDA has the tools and the knowledge to do it.”
In February, Florida officials detected screwworm larvae in an imported horse from Argentina as the animal made its way through the required import process. However, officials assured no case of screwworm had been detected outside of the quarantine area or in any Florida-based animal.
Reporting in the Rio Grande Valley is supported in part by the Methodist Healthcare Ministries of South Texas, Inc.
This article first appeared on The Texas Tribune.
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