New World screwworm fly The USDA confirmed Wednesday that the parasite has arrived in South Texas, marking the first time in decades that the parasite containing flesh-eating larvae has threatened the nation’s livestock industry, and only the third time it has appeared in the United States during that time.
Agriculture Secretary Brock Rollins said the case was in a three-week-old calf in La Priore, Texas, about 50 miles (80 kilometers) from the Mexico border. Texas state veterinarian Bud Dinges said he has created a 12-mile (20-kilometer) quarantine zone, prohibiting the movement of any warm-blooded animal — including pets — outside that zone without inspection.
No other fly has been discovered in the United States, Rollins said, and officials were quick to say that although the fly’s larvae pose a threat to animal production, they do not infect food. If treated properly, even an injured calf should recover, Rollins said.
Rollins, U.S. and Texas agriculture officials and livestock industry leaders have issued public alarms about the fly Movement through Mexico For more than a year, driven by memories that it caused tens of millions of dollars in losses — perhaps billions of today’s dollars — before it was eliminated in the 1970s.
This is the first confirmed case in Texas since 1966, Rollins said.
Months of efforts to keep the fly away from the United States included dropping millions of sterile screwworm flies into the area to mate with wild females — the same method used successfully before the fly was eradicated. Rollins said the USDA is confident enough in its preparations that it believes there is “no threat of a mass invasion.”
“There is no reason to believe that this incursion will lead to the spread of the scourge in our country,” Rollins said.
The announcement of the suspected case comes just a day after Rollins held an online news conference to highlight how close the threat is, with cases confirmed in Mexico as close as 25 miles (40 km) from the border — and to outline the USDA’s efforts to combat it.
The New World screwworm fly is a tropical species that has infected livestock for decades in warm weather throughout the southern United States, but has been contained in Panama until late 2024.
The female fly lays its eggs in open wounds or mucous membranes, and the eggs hatch into flesh-eating larvae – making them unlike most fly species – and can infect livestock, wild mammals, household pets and even humans. The infection can lead to death if left untreated.
In August 2025, federal health officials confirmed the case In a resident of Maryland Who traveled to El Salvador, but the victim recovered and officials did not find any transmission of the parasite. Before that, the last outbreak in the Florida Keys was in September 2016, mostly among wild deer, and was contained early the following year without spreading further.
Female flies mate once during their months-long life, and if they do so with a sterile fly, their eggs will not hatch, and their numbers will die out over time. Past fly eradication efforts were so successful that the United States closed sterile fly breeding facilities, leaving only one in Panama for decades.
This is changing. The USDA has allocated $21 million to convert a fruit fly breeding facility in southern Mexico into a screwworm fly breeding facility. A new center for dispersing sterile flies They were bred elsewhere in South Texas and began a $750 million screwworm fly factory there. Rollins said the breeding facility in Mexico should be up and running next month.
Officials have also deployed 8,000 fly traps along the U.S.-Mexico border, and Rollins said the USDA has tested more than 58,000 fly samples, along with 19,000 wild animals.
Rollins also closed the U.S.-Mexico border last year to livestock imports from Mexico, a decision she defended during her news conference Tuesday. Officials noted that the fly can also travel with people, their pets, and with wild animals, but Rollins confirmed Wednesday evening that it does not fly large distances on its own.
Ranchers and pet owners need to understand that it is important to respect the quarantine zone, Dinges said.
“Please help us prevent any further movement of this scourge by staying put,” he said.