Ag reported Allison Eliason wrote about the importance of preventing and managing screwworm in cattle populations several months back when cases began to reappear.  Since then, concerns have only increased as U.S. cases have now been reported.

On June 3, 2026, the USDA confirmed the first U.S. case of New World screwworm in more than 60 years when larvae were found in a calf in Zavala County, Texas. A second infected calf was confirmed nearby two days later. State and federal officials established movement restrictions, expanded trapping and surveillance programs, and increased sterile-fly releases in the area.  Concern had been raised about decreased federal preparedness under the current administration, and reduction in support for disease control programs in neighboring countries.

The New World screwworm is a parasitic fly whose larvae feed on the living tissue of warm-blooded animals, including cattle, horses, wildlife, pets, and, in rare cases, humans. Unlike ordinary maggots that consume dead tissue, screwworm larvae invade healthy flesh, creating painful wounds that can become fatal if left untreated. 

Screwworm was once one of the most destructive livestock pests in the United States. After decades of eradication efforts, the U.S. eliminated the pest in 1966 through the use of the Sterile Insect Technique, in which billions of sterilized male flies were released to prevent reproduction. The program was considered one of the greatest successes in agricultural pest control and pushed the pest south through Mexico and into Central America. 

For many years, a biological barrier maintained by the United States and Panama helped keep screwworm from moving north. However, beginning in 2023, a new outbreak spread through Central America and Mexico, raising concerns among livestock producers and animal health officials. 

The situation has become more serious in 2026. After moving steadily north through Mexico, screwworm was detected within a few dozen miles of the U.S. border, prompting the USDA to close southern ports of entry to livestock imports and intensify surveillance efforts. The USDA has also been releasing approximately 100 million sterile flies per week in Mexico and along the border to suppress the pest’s spread. 

On June 3, 2026, the USDA confirmed the first U.S. case of New World screwworm in more than 60 years when larvae were found in a calf in Zavala County, Texas. A second infected calf was confirmed nearby two days later. State and federal officials established movement restrictions, expanded trapping and surveillance programs, and increased sterile-fly releases in the area.

The primary concern is economic rather than food safety. Screwworm infestations can cause severe losses to cattle, sheep, goats, horses, and wildlife populations, potentially costing the livestock industry billions of dollars if the pest becomes reestablished in the United States. Ranchers are being urged to monitor animals closely for unusual wounds or maggot infestations and report suspected cases immediately. Officials emphasize that the current detections are being aggressively contained and that the decades-old eradication tools remain available and effective.

Ranchers are already facing pressures from what is expected to be a very dry year, sustained high fuel and materials costs, and an overall skittish market.  Widespread infestations would be catastrophic, and the abatement and control measures will be extremely urgent going forward.