Screwworm Found in Texas Decades After Eradication

The New World screwworm (Cochliomyia hominivorax), a flesh-eating parasitic fly that was largely eradicated from the United States in the 1960s, has been confirmed in a 3-week-old calf in Zavala County, Texas, marking the first detection in the state since 1966. The U.S. Department of Agriculture confirmed the case on June 3, triggering an urgent response that includes a 12-mile quarantine zone, deployment of sterile flies, and activation of a unified Incident Command Team.

A Pest Unlike Any Other

Unlike most maggots that feed on dead tissue, New World screwworm larvae burrow into the living flesh of warm-blooded animals. Female flies lay 200 to 300 eggs at a time in open wounds or mucous membranes, and the hatched larvae feed on healthy tissue, causing deep, festering, and potentially fatal wounds. The pest primarily affects livestock but can also infect pets, wildlife, and, in rare cases, humans.

Agriculture Secretary Brooke Rollins said the infected calf was found in La Pryor, Texas, approximately 50 miles from the Mexico border. Texas State Veterinarian Bud Dinges has established a 12-mile (20-kilometer) quarantine zone prohibiting the movement of any warm-blooded animal — including pets — outside that zone without inspection. Officials emphasized that there have been no further detections in the U.S. and that the country’s food supply remains safe, as screwworms do not infest meat, fruits, or vegetables.

A Decades-Old Threat Returns

The screwworm was once endemic to the southern United States but was declared eradicated in 1966 through the Sterile Insect Technique (SIT), a method that involves mass-rearing and releasing sterilized male flies. Since female screwworms typically mate only once, mating with a sterile male produces no offspring, causing the population to collapse over time. The method was so successful that the U.S. eventually shut down its domestic sterile fly breeding facilities.

However, the biological barrier that had contained the pest at the Darién Gap — a remote rainforest region at the border of Panama and Colombia — was breached in 2022. Scientists believe multiple factors contributed, including interruptions in sterile fly production during the COVID-19 pandemic and illegal cattle imports stemming from surveillance gaps. Since then, the flies have advanced through Central America and Mexico, with cases confirmed in Panama, Costa Rica, Nicaragua, and Mexico before reaching Texas.

As Ars Technica reported, the detection follows months of warnings. On May 28, a case was found just 25 miles from the U.S. border in a 5-year-old goat in Coahuila, Mexico. The USDA had already deployed 8,000 fly traps along the border and tested over 58,000 fly samples and 19,000 wild animals in preparation.

Economic Stakes for Texas and the Nation

The detection poses a serious threat to Texas’s $15 billion cattle industry, the largest in the nation. According to USDA estimates cited by the Texas Tribune, an outbreak could cause up to $1.8 billion in damage to Texas’s economy alone. The threat comes at a precarious time: the U.S. cattle herd is at its lowest level in 75 years, and beef prices are already at record highs.

Newsweek reported that any spread of the pest could further shrink cattle supplies and exacerbate price pressures on consumers. The USDA closed the U.S.-Mexico border to live cattle imports in May 2025 to prevent the pest’s spread, a move that has already strained supply chains.

Response and Containment Efforts

The USDA has invested $100 million into research, traps, and mounted patrol officers at the border. A $750 million sterile fly production facility is under construction in Edinburg, Texas, with an expected opening in fall 2027. A facility in Metapa, Mexico, is expected to begin operations in July 2026. Currently, 100 million sterile insects are dispersed per week in Mexico and along the U.S.-Mexico border.

“The United States has defeated this pest before, and we will do it again,” said Dudley Hoskins, USDA Under Secretary for Marketing and Regulatory Programs, in the agency’s press release. “Protecting our livestock industry is a national security issue of the utmost importance.”

However, tensions have emerged between state and federal officials over the response. Texas Agriculture Commissioner Sid Miller criticized the USDA’s response as “slow, bureaucratic and incomplete,” urging deployment of the Screwworm Adult Suppression System, which the USDA has called outdated and potentially carcinogenic. State Rep. Don McLaughlin (R-Texas) called for a Texas-led emergency response, saying, “For more than a year, I have joined Texas ranchers in sounding the alarm while federal regulators have moved at a snail’s pace.”

What to Watch For

Officials are urging ranchers and pet owners in the affected area to monitor animals for signs of infestation, including foul-smelling wounds with visible maggots, unusual restlessness, and lesions that fail to heal. The FDA has issued multiple emergency authorizations for treatments including topical sprays, powders, injectable drugs, and ointments.

Rollins expressed confidence in the containment effort, stating, “There is no reason to believe this incursion will result in establishment of the pest in our country.” Yet the breach of the Darién Gap barrier and the pest’s rapid northward advance raise questions about whether climate change, human movement of livestock, and pandemic-related disruptions have created new vulnerabilities that could make future incursions more likely.