The New World screwworm fly poses a significant threat to the $113 billion U.S. cattle industry. This threat has re-emerged for the first time in over fifty years, with confirmed cases in south Texas. The infestation was initially discovered in a 3-week-old calf in La Pryor, Texas, located about 100 miles southwest of San Antonio and 50 miles from the U.S.-Mexico border.
Impact on Texas
Texas, which holds a $17 billion share of the nation’s cattle, faces the greatest risk. Authorities have been working to prevent the spread of this parasite, given its potential impact. The pest was detected in Mexico in late 2024, rekindling fears as it spread beyond Panama. The last Texas outbreak was recorded in 1966.
Characteristics and Threats
The New World screwworm fly and its Old World counterpart are unique among flies. Their larvae consume live flesh rather than decaying materials. Females lay eggs in wounds and mucous areas. All warm-blooded animals, including wildlife, pets, and humans, are susceptible. Livestock face heightened risks from routine handling practices that might cause wounds. Even minor injuries, such as tick bites, can lead to infestation.
Without treatment, infestation can lead to death; however, multiple treatments are approved for use across species. Historically, the fly has cost ranchers tens of millions of dollars, which translates to potentially billions today.
Response to the Threat
Authorities remain vigilant, noting that the fly does not affect food safety. Agriculture Secretary Brooke Rollins reassured the public that beef production remains stable, a relief given current record consumer prices. Officials have been monitoring the pest’s movement through Mexico. An ongoing cooperative program between the U.S. and Panama aims to curb its spread.
According to Edward Burgess, a University of Florida entomologist, the fly reproduces rapidly, often spread by wildlife hosts such as deer. While sterile fly programs have historically mitigated infestations, these programs have largely ended outside of Panama.
Impact Outside the U.S.
The U.S. Centers for Disease Control and Prevention reported that more than 171,700 animals and 2,000 humans in Central America and Mexico have been affected as of June 2. The pests caused ten human deaths. Efforts to restrict livestock movement across the border began in May 2025.
Both climate change and less severe cold weather contribute to the fly’s expanding habitat. Warm temperatures bolster their survival in previously untenable environments.
Efforts and Measures
In Texas, a 12-mile quarantine zone was established in much of Zavala County. Inspections are mandatory for animals leaving this area. Authorities are vigilantly monitoring potential spread among regional wildlife.
Proactive measures include administering preventative injections and careful wound treatment. Since February, the USDA has been deploying sterile flies from a Texas center. They release approximately 4 million flies weekly. These tactics aim to diminish the fly’s numbers, given females mate only once, and sterile males ensure no hatching of eggs.
The USDA is enhancing sterile fly production capabilities. It invested $21 million in a Mexican facility, opening next month, and plans to launch a center in Texas next fall capable of producing up to 300 million sterile flies weekly.
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