Texas Faces New Challenges with New World Screwworm Outbreak

Texas authorities have confirmed two additional cases of the New World screwworm fly, highlighting the challenges in controlling a pest that threatens the U.S. livestock industry. The Department of Agriculture announced these findings on Monday.

The screwworm is not a traditional worm but a type of fly. Its larvae consume live flesh rather than dead tissue. Female flies lay eggs in open wounds of warm-blooded animals, such as livestock. However, wildlife, pets, and even humans may also become infested.

The recent cases involved a calf and a dog located hundreds of miles apart in La Salle and Andrews counties, respectively. This brings the total confirmed cases to four. Initially, the screwworm was discovered last week in a three-week-old calf, with a second case found nearby in another young calf.

“While addressing these cases that demand immediate attention and continuing to test suspected cases, we are concurrently working to completely eradicate the pest,” stated Dudley Hoskins, the department’s assistant secretary of marketing and regulation.

Until its eradication in the U.S. in the 1960s, the screwworm was an annual warm-weather scourge for ranchers. Since the pest was detected in Mexico at the end of 2024, both the department and the U.S. livestock industry have been striving to prevent further infestation, as it had been confined to southern Panama for decades.

The government’s control strategy involves breeding sterile male flies, which mate with wild females that only mate once in their lifetime. This prevents females from producing offspring, eventually curbing outbreaks. The department plans to increase sterile fly production at facilities outside the U.S. while constructing a fly factory in Texas.

Agriculture Secretary Brooke Rollins is scheduled to receive updates on the infestation on Monday afternoon at the Livestock Insects Research Laboratory in Kerrville, Texas.