New Threat to U.S. Cattle Industry: The Screwworm Infestation

The New World screwworm fly presents a significant threat to the U.S. cattle industry, valued at $113 billion. An infestation involving flesh-eating larvae has emerged in south Texas, marking the first occurrence in over fifty years. The infestation was traced to 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.

Efforts to prevent this infestation had been proactive. The state holds $17 billion worth of the nation’s cattle, making it the leading region in the industry. Despite containment strategies, the flies appeared in Mexico late in 2024. Historically, these flies plagued ranchers from the 1930s through the 1960s until eradication was achieved by releasing sterile male flies.

Understanding the Screwworm Fly Threat

The New World screwworm fly is unique as its larvae consume live flesh and fluids, unlike other flies that target dead material. Females lay eggs in wounds and mucous membranes after mating once in their lifespan. All warm-blooded animals, including wildlife, pets, and humans, are susceptible.

Livestock are especially vulnerable due to standard handling practices that cause skin injuries. According to Lee Haines, associate research professor at the University of Notre Dame, procedures like shearing, de-horning, and moving cattle contribute to exposure. Even minor wounds, such as from tick bites, can lead to infestation.

“Even the smallest wounds can put cattle at risk,” said Stephen Diebel, Texas rancher.

If left untreated, infestations can lead to death, though several treatments are approved for various species.

Impact on Beef Production

Agriculture officials emphasize that the screwworm fly does not contaminate food, and beef production is unlikely to suffer damage. This is especially relieving at a time when consumers are facing high beef prices.

Preventive Actions and Challenges

The movement of the fly through Mexico toward the U.S. had been a concern for nearly two years. The fly showed up in southern Mexico in November 2024, prompting action as previous outbreaks were considered eradicated. Edward Burgess, a University of Florida entomologist, noted the fly’s rapid reproduction and ability to spread.

Outside the U.S., the parasite impacted over 171,700 animals and 2,000 humans throughout Central America and Mexico, according to the CDC. The screwworm fly thrives in warmer climates, which are expanding due to climate change.

Containment Measures in Texas

Texas State Veterinarian Bud Dinges established a quarantine zone covering parts of Zavala County. Inspections are required for animals leaving the zone to prevent further spread.

Local ranchers are worried about potential transmission to wildlife, particularly deer. A previous outbreak occurred in the Florida Keys in 2016.

Strategic Responses

Ranchers are taking preventive measures, including administering injections against infestations. Additionally, they are meticulously treating cattle wounds and monitoring for illness. The USDA has intensified efforts by dropping sterile flies in south Texas since February, now distributing twice weekly, totaling 4 million flies.

Despite the swift deployment, the slow breeding rate of sterile flies post-Panama shutdowns prompted further action. The USDA invested $21 million in a fly-breeding facility in southern Mexico, operational next month.

Plans for a state-of-the-art fly factory in southern Texas are underway, with an expected capacity of 300 million sterile flies weekly. Operations will commence next fall.