Screwworm Parasite Spreads Beyond Texas, Threatens Farms

The New World screwworm — a flesh-eating parasite not seen in the United States since the 1960s — has spread beyond Texas into New Mexico, with five confirmed cases now detected across two states, according to the U.S. Department of Agriculture. The resurgence threatens to inflict billions of dollars in damage on the nation’s cattle industry and has triggered an escalating emergency response from state and federal officials.

The Growing Outbreak

As of June 9, 2026, authorities have confirmed five cases: three calves and a goat in Texas, and a dog in Lea County, New Mexico — marking the first screwworm case detected outside Texas. The first case was discovered on June 3 in a three-week-old calf in Zavala County, Texas. A second case followed on June 5 in a one-month-old calf just 5.6 miles away. Over the weekend of June 8-9, three additional cases were announced: a calf in La Salle County, a goat in Gillespie County, and the dog in New Mexico.

Crucially, the infected dog in New Mexico had not traveled to Mexico or Texas, suggesting that local fly populations may have already become established, according to New Mexico State Veterinarian Samantha Holeck. In response, 12-mile (20-kilometer) quarantine zones have been established around each confirmed case location to restrict animal movement.

What Is New World Screwworm?

The New World screwworm (NWS) is the larval stage of the fly Cochliomyia hominivorax. Unlike common maggots that feed on dead tissue, screwworm larvae burrow into and consume living flesh. Female flies lay eggs in open wounds of warm-blooded animals — including cattle, wildlife, pets, and occasionally humans. The larvae enlarge the wound, causing severe tissue damage, secondary infections, and death within weeks if left untreated.

As The Guardian reported, the USDA has emphasized that the U.S. food supply remains safe, as screwworms do not infest meat, fruits, or vegetables.

A 60-Year Success Story Unravels

The screwworm was considered one of the greatest achievements in agricultural pest control. The USDA developed the Sterile Insect Technique (SIT) in the 1950s, a method where male flies are sterilized via irradiation and released in massive numbers. Since female screwworm flies mate only once in their lifetime, mating with a sterile male produces unfertilized eggs that never hatch. The program successfully eradicated NWS from the U.S. by 1966 and maintained a barrier zone in Panama for decades.

But the pest began moving northward from Central America in 2023, reaching Mexico in late 2024. Despite USDA preparations — including closing ports of entry to Mexican cattle and dropping over 130 million sterile flies in Texas since January — the parasite has now crossed the border.

Economic Stakes Are Enormous

Texas is the dominant cattle-producing state in the U.S., and the stakes could not be higher. According to USDA estimates cited by the Texas Tribune, a full outbreak could cause $1.8 billion in damage to Texas’ economy alone. The threat extends beyond cattle: the state’s multi-billion-dollar white-tailed deer hunting industry is also at risk.

Beef prices are already near record levels due to a reduced national cattle herd — now at a 75-year low. Canada temporarily stopped importing cattle, horses, and other livestock from Texas on June 5, adding further economic pressure.

The Response: Sterile Flies vs. Poison Bait

The primary federal strategy relies on the Sterile Insect Technique. The USDA currently produces about 100 million sterile flies per week at the COPEG facility in Panama, with flies dispersed from a facility at Moore Air Base in Edinburg, Texas. A new $750 million production facility is under construction at Moore Air Base, with initial production expected by November 2027 — though Governor Greg Abbott is pushing for completion by May 2027.

“Here is the reality of this cycle. This is likely to spread over the course of the summer,” Abbott said, according to the Texas Tribune via KSAT. “During winter months, it may kill off the flies or reduce their number, but we can’t make it through a second summer.”

However, the sterile fly approach has its critics. Texas Agriculture Commissioner Sid Miller — who lost the recent Republican primary — advocates using poison bait instead, arguing the federal strategy will take too long. “What the hell is a good fly?” Miller asked in an interview with AP News, questioning the focus on sterile flies over faster-acting poison methods. The USDA and other experts caution that the bait has not been proven effective and could harm other species.

Political Dimensions

The outbreak has become politically charged. USDA Secretary Brooke Rollins blamed Biden-era “open border” policies for enabling cattle movement from Mexico, saying “these flies do not fly to new areas on their own.” But local officials like Val Verde County Judge Lewis Owens dispute this, noting that cattle imports were shut down multiple times under both administrations. “So, let’s not keep blaming individuals or blaming other parties,” Owens said.

Meanwhile, the response has become an issue in the Texas governor’s race. State Representative Gina Hinojosa, a Democrat running against Abbott, has called for a public hearing on the screwworm response.

What Comes Next

Scientists expect more cases in the coming days and weeks as surveillance intensifies and summer conditions — the parasite prefers humid areas above 77°F (25°C) — favor its spread. Edward Burgess, a University of Florida entomologist, noted that increased vigilance is leading to more detections. “When that first case is seen, everyone is being vigilant and their eyes are on it more intensely,” he told AP News.

Winter 2026-27 may kill off some flies, but a full eradication effort will require sustained sterile fly releases through 2027. Mexico’s renovated facility in Metapa is expected to begin production in summer 2026, which could help bridge the gap until the Texas facility reaches capacity.

For now, Texas officials are urging ranchers to monitor their herds closely and report any suspicious wounds. A 24-hour screwworm hotline and online case map are now available. As Texas Farm Bureau President Russell Boening put it: “Texas livestock producers and all Texans must now be vigilant in their efforts to manage and combat the invasive pest.”

The return of a pest that was once declared eradicated — and that had been held at bay for six decades — marks a sobering moment for American agriculture, with the full scale of the threat still unfolding.