New World Screwworm Threatens South Texas Livestock

The New World Screwworm, a parasitic fly affecting livestock and other warm-blooded animals, has been detected in South Texas. The USDA’s Animal and Plant Health Inspection Service confirmed on June 3 that larvae were found in a calf in Zavala County, Texas. As of June 11, there were six confirmed cases.

Screwworm larvae burrow into living animals, causing significant damage and economic losses. While they don’t make meat unsafe, they threaten to increase beef prices already at a record high.

U.S. Secretary of Agriculture Brooke Rollins announced on May 11, 2025, the suspension of live cattle, horse, and bison imports through southern U.S. ports due to the screwworm’s spread in Mexico. An APHIS strike team is already in Texas, employing measures like releasing sterile male flies to control the spread.

Efforts to combat this pest began in the 1920s and 1930s. The Screwworm Adult Suppression System uses insecticide-laced bait and sterile male flies to prevent reproduction, a method declared successful in eradicating the pest in 1966.

Despite these efforts, screwworms have advanced rapidly through Mexico. Texas Agriculture Commissioner Sid Miller criticized the USDA for moving too slowly and missing key components in their strategy. He advocated for a more robust response, urging the president to cut bureaucracy and utilize all available resources.

Texas Land Commissioner Dawn Buckingham highlighted the threat to livestock and wildlife. Her office has offered resources and land access to assist in the government’s response. Buckingham stressed the importance of quick action and collaboration, noting past successes in combating screwworms and the availability of treatment and prevention methods.

The screwworm’s spread poses challenges due to increased global mobility, which facilitates the transfer of insects. However, with known solutions and international cooperation, officials remain hopeful of controlling the outbreak effectively.