A flesh-eating parasite that has not been seen in the United States for nearly 60 years has been confirmed in a calf in southern Texas, marking a significant concern for the country's livestock industry. The New World screwworm fly was detected in an animal located approximately 50 miles from the Mexico border, according to Agriculture Secretary Brooke Rollins.
The parasite was eradicated from the U.S. in the 1970s after causing tens of millions of dollars in losses. Its return comes at a challenging time, as food prices, particularly for beef, are at record highs across the country. While the flies pose no direct threat to food safety, officials worry that an outbreak could create cattle and poultry shortages.
The New World screwworm fly's larvae feed on the blood of warm-blooded animals. Female flies target open wounds to lay eggs, and when the larvae hatch, they rapidly consume blood and flesh from the host. Untreated infestations can kill animals within days. Although the risk to humans is considered low, the parasite can spread quickly in areas with large concentrations of livestock.
For over a year, the USDA and Texas officials have been warning livestock owners about the parasite's advancement through Mexico. The insect has traveled more than 1,100 miles from southern Mexico before reaching Texas. In August 2025, federal health officials confirmed one case in a Maryland resident who had traveled to El Salvador, though that person recovered with no further transmission detected.
Rollins stressed that the Texas case represents the first confirmed detection in the state since 1966 and the only case identified so far. "There is no threat of mass infestation," she said. "There is no reason to believe this incursion will result in establishment of the pest in our country."
Texas Agriculture Commissioner Sid Miller criticized the federal response, stating that despite the USDA's existing plan and the release of billions of sterile flies, the screwworm has continued advancing. The standard eradication strategy involves the sterile insect technique, where sterilized male flies are released to disrupt breeding cycles. Female screwworm flies mate only once in their months-long lives, so eggs from sterile partners do not hatch, reducing the population over time.
Miller urged the Trump administration to deploy the screwworm adult suppression system more aggressively. This approach uses attractants, bait, and targeted insecticides to reduce adult fly populations before sterile fly releases are used to complete eradication efforts.
In March, Rollins announced that the USDA had partnered 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 efforts were so successful that the U.S. eventually shut down its sterile fly breeding facilities, leaving only one operation in Panama for decades.