A New World screwworm fly infestation has been confirmed in Texas, marking the first occurrence in the state since 1966. The discovery was made in a 3-week-old calf in La Pryor, Texas, approximately 100 miles southwest of San Antonio and 50 miles from the U.S.-Mexico border. This parasitic fly, known for its flesh-eating larvae, poses a significant threat to the $113 billion U.S. cattle industry, with Texas alone housing $17 billion worth of cattle.
Threat to Livestock and Industry
The larvae of the New World screwworm fly feed on live flesh and fluids, making them particularly dangerous to livestock. Females lay eggs in open wounds and mucous membranes, and infestation can lead to severe health issues or death if untreated. Cattle are especially vulnerable due to common handling practices that cause skin breaks, such as shearing, de-horning, and moving them between corrals. Birth also exposes both mother and calf to risk.
'Even wounds as small as a tick bite can put cattle at risk,' said Stephen Diebel, a Texas rancher and president of the Texas & Southwestern Cattle Raisers Association.
Historical Context and Response Efforts
The screwworm fly was a major pest for cattle ranchers from the 1930s through the 1960s until eradication efforts led by the USDA successfully contained the parasite. The strategy involved breeding sterile male flies and releasing them to mate with wild females, effectively reducing the population. However, recent outbreaks in Mexico and Central America have reignited concerns.
Federal and state officials have been on high alert since November 2024 when cases were confirmed in southern Mexico. Agriculture Secretary Brooke Rollins emphasized that the infestation is unlikely to impact beef production significantly, offering some reassurance to consumers already facing record prices.
Broader Implications
The reappearance of the screwworm fly in Texas underscores the challenges of controlling invasive species across borders. With programs producing sterile flies largely shut down outside Panama, the rapid reproduction and mobility of the fly complicate containment efforts.
As of June 2025, the parasite has sickened over 171,700 animals and 2,000 people across Central America and Mexico, with 10 human deaths reported. Authorities continue to monitor and respond to the infestation to protect both animal and human health.