The New World screwworm, a fly whose larvae feed on the tissues of livestock, wildlife and pets, was detected in a three-week-old hatchling in La Pryor, Texas, the Department of Agriculture confirmed Wednesday night. It is the first case found in cattle in the United States since the insect was eradicated from the country in the 1960s.
“We are taking immediate action this afternoon and tonight to deploy, contain and eradicate this case of New World screwworm in South Texas,” Agriculture Secretary Brooke Rollins said at a news conference.
If more screwworms are found beyond a single case, the infections, which can kill if left untreated, could devastate the U.S. livestock industry.
The Department of Agriculture has been preparing for months for the reappearance of the screwworm in the United States. By the mid-2000s, the screwworm had been eradicated from all of North and Central America, but the parasite has been moving north and was detected on the Mexico-Guatemala border in November 2024.
Screwworm flies don’t move very far, but they spread with the movement of unknowingly infected animals, especially if they are trucked to a new location. According to the Department of Agriculture, more than 20,000 cases have been detected in Mexico, and Mexican cattle have been banned from entering the United States for more than a year.
Screwworm flies do not infest fruits or vegetables, and the Department of Agriculture says its Food Safety and Inspection Service will ensure that all meat, poultry and eggs are safe for consumption.
The Department of Agriculture has declared a 20-kilometer quarantine “infested zone” where the infected calf was found, increasing surveillance and limiting the movement of all warm-blooded animals out of that zone. The department has also sent veterinarians and animal health officials to the area, as has the Texas Animal Health Commission.
Authorities are also dispersing millions of sterile New World screwworm flies, by air and by truck, in the area. Releasing sterile flies, which mate with wild female flies and drive the population toward eradication, is the only way currently to control the spread of the fly.
Only one facility, in Panama, produces sterile flies: around 100 million per week. The U.S. Army Corps of Engineers recently broke ground on a $750 million production facility at Moore Air Force Base in Edinburg, Texas. The facility is expected to begin producing 100 million sterile flies per week by the end of 2027, and then up to 300 million per week thereafter.
