Flesh-eating screwworm may have been detected in South Texas, USDA says

A screwworm fly stands on a branch of a plant at a bio-factory in Metapa de Dominguez, Mexico, October 17, 2025. An infestation of the flesh-eating screwworm parasite may have been detected in South ​Texas, and a sample is at a federal government laboratory for testing, the U.S. Department of Agriculture said on Wednesday.

A screwworm fly stands on a branch of a plant at a bio-factory in Metapa de Dominguez, Mexico, October 17, 2025. An infestation of the flesh-eating screwworm parasite may have been detected in South ​Texas, and a sample is at a federal government laboratory for testing, the U.S. Department of Agriculture said on Wednesday. (Daniel Becerril, Reuters)


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KEY TAKEAWAYS
  • USDA tests samples for flesh-eating screwworm in South Texas; results pending.
  • Texas Rep. McLaughlin shared unverified photos of larvae in cattle wounds.
  • The potential outbreak could shrink U.S. cattle supply, raising beef prices significantly.

MEXICO CITY — An infestation of the flesh-eating screwworm parasite may have been detected in South ​Texas, and a sample is at a federal government laboratory for testing, the U.S. Department of Agriculture said on Wednesday.

Samples from two calves on a cattle ranch in La Pryor, Texas, were taken on ‌Tuesday and sent to a federal lab in Iowa, Texas Representative Don McLaughlin told Reuters earlier, adding he had seen photos and videos of the animals.

"We ⁠will provide updates the moment results are available," USDA ​said on X. "We have already activated personnel on the ⁠ground and are working with local partners."

Widespread market chatter about the suspected case hung over cattle futures, which traders said ‌have long been sensitive to ‌threats of New World screwworm. The parasite has been moving north through Mexico for more than ⁠a year. Market players believe a screwworm infestation in the U.S. could ⁠reduce demand for beef from consumers nervous about the flesh-eating pest, but would be bullish in the long term by reducing the U.S. cattle supply.

A photo seen by Reuters, which McLaughlin said was one of those he also saw, shows multiple larvae resembling the screwworm inside a bloody circular wound on an animal. McLaughlin said one of the suspected infestations was detected in an umbilical cord wound of a calf, though it was ‌unclear if that was the case seen in the photo. Reuters could not ​immediately verify the photo.

"At this point, it's unconfirmed that it's the New World screwworm," McLaughlin, a Republican, said. "It looks like it, but it's unconfirmed."

Outbreak could shrink U.S. cattle supply

The Texas Animal Health Commission told Reuters on Wednesday there has been no confirmed case of New World screwworm in Texas.

Screwworms are parasitic flies whose females lay eggs in wounds of any warm-blooded animal. Once the eggs hatch, hundreds of screwworm larvae use their sharp mouths to burrow through living flesh, eventually killing their host if left untreated. An outbreak of screwworm in the U.S. ​could cause $1.8 billion in damage to Texas' economy alone and would likely raise U.S. beef prices by shrinking the U.S. cattle supply, experts ‌have said.

Earlier in ‌the week, the USDA ⁠said that McLaughlin, who had said a case was confirmed one mile south of the Texas border, had inaccurate information. The USDA confirmed a case 25 miles south of the Texas border in Coahuila state on Tuesday.

The U.S. has kept its border with Mexico closed to cattle imports for more than a year to prevent the destructive parasite from reaching U.S. ‌border states. The United States ​has spent millions of dollars to slow its advance through Mexico, investing ‌in sterile fly production facilities, ⁠expanding trapping efforts and ​increasing livestock surveillance.

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The Key Takeaways for this article were generated with the assistance of large language models and reviewed by our editorial team. The article, itself, is solely human-written.

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Cassandra Garrison, Heather Schlitz and Tom Polansek

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