Screwworm Fly Threatens Texas Cattle Industry After Decades

The New World screwworm fly has appeared in south Texas, confirmed by the U.S. Department of Agriculture on Wednesday. This is the first instance in decades where this parasite, with larvae that consume flesh, poses a threat to the U.S. cattle industry. Agriculture Secretary Brooke Rollins reported the case in a 3-week-old calf in LaPryor, Texas, located about 50 miles from the Mexico border. Texas State Veterinarian Bud Dinges has established a 12-mile quarantine zone, prohibiting the movement of warm-blooded animals, including pets, without inspection.

Rollins noted no other detections in the U.S. and emphasized that while the larvae threaten livestock, they do not infest food. With proper treatment, the infested calf should recover. U.S. and Texas officials, along with cattle industry leaders, had been warning about the fly’s proximity in Mexico, remembering its past economic damage before eradication in the 1970s.

This marks the first case confirmed in Texas since 1966. The USDA has taken proactive measures by releasing sterile screwworm flies over the area to mate with wild females, a previously successful method. Rollins expressed confidence in the preparations, which aim to prevent a mass infestation.

The confirmation of this case follows Rollins’ recent online news conference, highlighting the severity of the threat. Cases in Mexico have been confirmed as close as 25 miles from the border. The screwworm fly, a tropical species, previously infested cattle in the southern U.S. until containment in Panama. Female flies lay eggs in wounds, leading to flesh-eating larvae, affecting livestock and other animals.

Infestations can prove fatal if untreated. A case in Maryland was confirmed in August 2025 in a traveler from El Salvador, with the individual recovering and no transmission found. The last outbreak occurred in Florida Keys in 2016 among wild deer but was contained.

The USDA is now investing heavily to revamp screwworm fly eradication efforts. With $21 million dedicated to transforming a fruit fly facility in Mexico for screwworm breeding, a new dispersal center in southern Texas was opened, and construction began on a $750 million factory. The breeding facility in Mexico is expected to operate soon.

Officials have placed 8,000 fly traps along the border and tested 58,000 fly samples along with 19,000 wild animals. Rollins defended closing the U.S.-Mexico border to livestock imports last year. While the fly doesn’t travel vast distances alone, it can move with people and animals.

Dinges stressed the importance of adhering to the quarantine to prevent further spread. “Please help us prevent any further movement of this pest by staying put,” he said.