Flesh-eating screwworm returns to Texas for first time since 1966

The U.S. Department of Agriculture confirmed four cases of the New World screwworm fly in Texas — the first detections in the state since 1966 — threatening the nation's $113 billion cattle industry, the Korea Times reported.

Texas holds $17 billion of the nation's cattle inventory, ranking first among all states, and the cases mark the first confirmed screwworm detections there since 1966. Officials had warned of the threat for nearly two years as the pest advanced north through Mexico toward the U.S. border.

Federal officials confirmed the initial case in a calf near La Pryor, about 100 miles southwest of San Antonio and 50 miles from the U.S.-Mexico border in Zavala County, according to the Korea Times. A second infection was found in a dog hundreds of miles away, and two additional cases were confirmed in La Salle and Andrews counties. Authorities placed a 12-mile quarantine zone around Zavala and Uvalde counties, setting up vehicle checkpoints to restrict livestock movement.

The screwworm fly deposits eggs in open wounds of warm-blooded animals; the resulting larvae tunnel into living tissue. "Any warm-blooded animal, including wildlife, pets and occasionally even humans, can be infested," the USDA said. Stephen Diebel, a Texas rancher and president of the Texas & Southwestern Cattle Raisers Association, warned that even wounds "as small as a tick bite" can put cattle at risk, the Korea Times reported.

The pest was eradicated from the U.S. by the 1960s through aerial releases of sterile male flies but resurfaced in Panama and spread north through Central America. The fly was detected in Mexico in late 2024. "It's hard to stay ahead of it because of how fast that fly is able to move and regenerate," said Edward Burgess, an entomologist at the University of Florida.

Lee Haines, an associate research professor of biological sciences at the University of Notre Dame, noted that ordinary livestock handling creates openings for infection. "Standard practices with cattle can break the skin, including shearing and dehorning, or even moving them in and out of corrals can cause scrapes and cuts," Haines told the Korea Times.

Agriculture Secretary Brooke Rollins closed the border to livestock entries in May 2025 to delay the pest's arrival. The USDA is now releasing 4 million sterile male flies twice weekly in south Texas, along with 4 million pupae per week. A $750 million fly-breeding facility capable of producing 300 million sterile flies weekly is under construction in southern Texas and scheduled to open this fall, and a $21 million facility in southern Mexico is set to open next month.

Outside U.S. borders, the screwworm has sickened more than 171,700 animals and 2,070 people across Central America and Mexico as of June 3 and claimed 10 human lives, the Korea Times reported.