The New World screwworm fly, a destructive parasite that feeds on living flesh, has been detected in several new locations, raising alarms among agricultural officials and livestock owners. The U.S. Department of Agriculture (USDA) confirmed three additional cases, including one outside the primary cluster in Texas, highlighting the challenges of containing this resurgent pest.
The screwworm fly larva, known for burrowing into open wounds of warm-blooded animals, poses a significant threat to cattle, wildlife, pets, and occasionally humans. The USDA has been working to control the spread through a program that breeds sterile male flies, which are then released to mate with wild females, a method that has successfully contained the pest in the past.
The Spread of the New World Screwworm Fly
As of Monday, there are five confirmed cases: three calves and a goat in Texas, and a dog in neighboring Lea County, New Mexico. Initially reported as a Texas case, the dog’s infestation was reclassified to New Mexico, with officials investigating the animal’s travel history. The first two cases were discovered last week in calves in south Texas, followed by a case in a calf in La Salle County and a goat in Gillespie County.
Edward Burgess, a University of Florida entomologist, noted that the increased vigilance following the initial case discovery might lead to more reported instances. “When that first case is seen, everyone is being vigilant and their eyes are on it more intensely,” Burgess said. “And when you are looking for something, you are more likely to see it.”
Efforts to Combat the Outbreak
The USDA and the U.S. cattle industry have been actively working to prevent a widespread infestation since the screwworm was detected in Mexico late in 2026. The parasite, which was eliminated in the U.S. in the 1960s, gets its name from the maggots’ habit of burrowing into wounds. Despite its reappearance, beef prices have not been significantly affected, as the parasite does not infest meat or fruit. There are also a dozen government-approved medications available to treat livestock.
Canada temporarily halted the import of cattle, horses, and other livestock from Texas on Friday, as the parasites thrive in humid areas with temperatures above 77°F (25°C). Burgess emphasized that the long-term solution—breeding sterile male flies—is still months away. The USDA is working to increase sterile fly production in plants outside the U.S. and is building a massive fly factory in Texas.
Controversial Solutions and Government Response
USDA Secretary Brooke Rollins announced that the goal is to have enough sterile flies to stop the pests from returning in 2027, after the winter kills off most of them. Scientists are also exploring ways to sterilize only male flies to enhance the program’s effectiveness. Texas officials have encouraged ranchers to monitor their herds and report any suspicious activity to a 24-hour hotline, with a website and map established to track reported cases.
Republican Gov. greg abbott emphasized the importance of immediate action, stating, “This is a highly treatable condition if you act on it immediately.” However, Texas Agriculture Commissioner Sid Miller criticized the federal response, arguing that it will take too long and risks crippling the cattle industry. Miller proposed using a poison bait to eliminate the screwworm problem within a few months, despite experts stating that the bait’s effectiveness is unproven and could harm other flies, animals, and even humans. “What the hell is a good fly?” Miller questioned in an interview.