New World Screwworm Fly Reappears in South Texas, Threatening Cattle Industry

Sat Jun 06 2026 20:01:18 GMT+0000 (Coordinated Universal Time)

U.S. officials confirm the first detected case of the flesh‑eating screwworm fly in decades, establishing a 12‑mile quarantine and rolling out sterile fly releases to eliminate the pest.

A three‑week‑old calf in LaPryor, Texas, tested positive for the New World screwworm fly, the parasite that once devastated cattle across the southern United States. Agriculture Secretary Brooke Rollins announced a 12‑mile quarantine, aggressive fly trapping, and a $21 million investment in a new breeding facility in Mexico to release sterile flies. The USDA is confident the incident will not lead to widespread infestation.

The first confirmed case of the New World screwworm fly in the United States in more than a half‑century was reported on Wednesday when a three‑week‑old calf in LaPryor, Texas, tested positive for the parasite. Agriculture Secretary Brooke Rollins said the calf was only 50 miles from the Mexico border, sparking a swift national response.

Veterinarian Bud Dinges announced a 12‑mile (20‑kilometer) quarantine zone around the infection site. Under the restriction, no warm‑blooded animal—ranch animals, pets or livestock—may leave the zone without a USDA inspection. The quarantine was the first active containment measure taken since 1966, when the fly was detected inside U.S. borders for the first time.

Rollins stressed that the fly’s larvae are lethal only to livestock and that, with prompt treatment, the affected calf should recover fully. She also noted that there have been no additional detections in the country and that “there is no reason to believe this incursion will result in establishment of the pest in our country.”

For months, federal officials have been fighting the likelihood of a mass infestation by reintroducing millions of sterile screwworm flies into affected areas. The sterile‑fly technique, proven in the 1970s when the U.S. eradicated the pest, has been pivotal in keeping the fly at bay. Rollins said that the USDA’s confidence in the method remains high despite the new intrusion.

Key to the strategy is the newly converted breeding facility in southern Mexico, which will produce sterile flies that can be released later this month. The $21 million investment was made to support the expansion of a fruit fly breeding plant into a screwworm fly factory. In parallel, the USDA has increased surveillance by deploying 8,000 fly traps along the U.S.–Mexico border and testing more than 58,000 fly samples, in addition to over 19,000 live animal samples.

Concurrent with the fly quarantine, Rollins reminded the public that the fly can spread through people, pets and wild animals moving across the border, but she emphasized that the insect does not travel long distances on its own. “Please help us prevent further movement of this pest by staying put,” rancher‑turned‑closet spoke to local media.

The New World screwworm fly is a tropical species that historically fed on the flesh of cattle in warm weather, leading to significant losses for the industry. The parasite is still a threat today, with previous outbreaks recorded in Mexico and as far as the Florida Keys. Modern tools—sterile fly releases, border containment and widespread testing—are part of the U.S.’s plan to keep the pest from establishing a foothold.