The New World screwworm fly, a parasitic menace that had been eradicated from the United States for over half a century, has made a troubling comeback. This flesh-eating fly was recently confirmed in a 3-week-old calf in La Pryor, Texas, sending shockwaves through the $113 billion U.S. cattle industry.
The infestation was discovered in a region critical to the cattle industry, with Texas being home to $17 billion worth of cattle. This resurgence comes after the deadly flies were detected in Mexico late in 2026, following years of containment at the southern end of Panama. The last confirmed case in Texas was in 1966, making this a significant and alarming event.
The Unusual Nature of the New World Screwworm Fly
The New World screwworm fly is unique among flies because its larvae, or maggots, feed on live flesh and fluids rather than dead material. Females lay their eggs in open wounds and mucous membranes after mating only once in their months-long lives. This behavior makes them particularly dangerous to livestockas standard practices like shearing, de-horning, and even moving cattle can create vulnerable wounds.
Any warm-blooded animal, including wildlife, pets, and occasionally humans, can be infested. The vulnerability of livestock is exacerbated by their handling practices, which can break the skin and create entry points for the fly’s larvae. Even minor wounds, such as those from a tick bite, can put cattle at risk.
The Impact and Response to the Infestation
The reappearance of the New World screwworm fly poses a significant threat to the cattle industry. While the fly does not infest food, the potential for widespread infestation could lead to substantial economic losses. In the past, ranchers faced tens of millions of dollars in losses, which would translate to billions in today’s dollars.
Federal and state officials have been sounding alarms for nearly two years, ever since the fly’s movement through Mexico was confirmed in November 2026. The fly’s rapid reproduction and spread, facilitated by its hosts such as wild animals, make it challenging to contain. Programs that produced and released sterile flies have largely shut down outside of Panama, further complicating efforts to control the infestation.
As of June 2, 2026, the parasite had sickened over 171,700 animals and 2,000 people across Central America and Mexico, with 10 human deaths reported. In response, Agriculture Secretary Brooke Rollins closed border entries to livestock in May 2026, which she credited with delaying the fly’s arrival in Texas by a year.
Quarantine and Prevention Measures
Texas State Veterinarian Bud Dinges imposed a 12-mile quarantine zone covering much of Zavala County and a small part of Uvalde County. Animals cannot leave this zone without being inspected. Local ranchers are concerned about the fly spreading among wildlife, particularly deer, as a similar outbreak occurred in the Florida Keys in 2016.
Ranchers are taking proactive measures, including giving injections that prevent screwworm infestation and treating wounds from ear tagging and other practices. The USDA has been dropping sterile flies in south Texas since February, releasing 4 million flies twice a week and placing an additional 4 million pupae in the ground weekly.
The USDA is confident in its preparations and believes there is no threat of mass infestation. However, the situation remains critical, and ongoing efforts are essential to contain and eradicate the New World screwworm fly.
