Federal and state officials confirmed the presence of the New World screwworm in a calf in southern Texas, approximately 50 miles from the Mexico border. This marks the first confirmed detection of the parasitic fly in the state since 1966 and represents a significant concern for the nation's cattle industry at a time when beef prices are at record highs.
The screwworm fly's larvae feed on the blood and flesh of warm-blooded animals like cattle. Female flies target open wounds to lay their eggs, and when the larvae hatch they quickly consume blood and tissue. Without treatment, infected animals will die. While the risk to humans is low, the parasite can spread rapidly in areas with large concentrations of livestock.
The United States successfully eradicated the screwworm in the 1970s after it caused tens of millions of dollars in losses. For more than a year, the USDA and Texas officials have warned ranchers about the parasite's advancement through Mexico, where it has traveled more than 1,100 miles from the south despite ongoing control efforts.
Texas Agriculture Commissioner Sid Miller expressed frustration with the USDA's response, stating that despite billions of sterile flies being dispersed, the screwworm still reached Texas. He argued the agency missed an important component of its containment strategy and called for increased deployment of the screwworm adult suppression system, known as Swass, which combines attractants, bait, and targeted insecticides.
Agriculture Secretary Brooke Rollins pushed back against concerns, insisting there is no threat of mass infestation and no reason to believe the parasite will become established in the country. She noted the Texas case was the only confirmed case so far.
The USDA has previously relied on releasing sterile male flies to break the breeding cycle, since female screwworm flies mate only once in their months-long lives and do not reproduce with sterile males. In March, Rollins announced the USDA would partner with the Army Corps of Engineers and Mortenson Construction to build a new sterile fly production facility at Moore Airbase in Edinburg, Texas.
Past eradication campaigns proved highly successful, leading the US to shut down most sterile fly breeding facilities decades ago, with only one remaining in Panama. In Mexico, high treatment costs have forced some ranchers to use crude measures like applying gasoline or lime to open wounds to remove worms.
The detection has prompted neighboring states to issue alerts and monitor for potential spread across state lines as officials work to assess the scope of the outbreak and prevent the parasite from establishing a permanent presence in the region.