Texas Cattle Ranchers Fear the Return of a Flesh-Eating Pest

Chris Womack is one of a dwindling number of Texas ranchers who can remember fighting the New World screwworm, a once-vanquished pest threatening to make an unwanted encore in the US after its recent return to northern Mexico.

“You never forget the smell,” Womack, 60, said of his first encounter with a calf being devoured by screwworm maggots. It was one of many he and his father would treat in the early 1970s as an outbreak of the parasite — which can kill cattle in less than two weeks — devastated Texas ranchers.

More than 50 years later, Womack and other Texas cattlemen are bracing for the screwworm’s potential comeback. Cases are proliferating in a Mexican state that borders Texas, with the pest having escaped containment by an international eradication program that banished it for decades. Texas Governor Greg Abbott issued a disaster declaration last week to open up state resources for the screwworm response.

The pest’s resurgence would squeeze the $130 billion US cattle industry, which is already struggling with a record-low herd and rising costs. The screwworm prompted the US to ban cattle imports from Mexico for much of the last 14 months, crimping American beef producers at a time when record prices for the meat are adding to the pressure on shoppers angry about the cost of food.

The eradication program, which depends on releasing enormous swarms of sterilized screwworm flies into the wild, can’t be fully revived in the short term. So Womack, who is also a veterinarian, said he’s worried ranchers in Texas will have to relearn the grisly, time-consuming work of protecting herds from the pest.

“There’s a generational ignorance – not stupidity, just ignorance,” said Womack, who raises red Angus cattle and sheep in San Angelo, about 200 miles (320 kilometers) northwest of Austin. “The young producers and young veterinarians have no experience with it. Why would they?”

Read more: A Forgotten Parasite’s Return Threatens US Livestock: Dispatch

Screwworm flies lay their eggs in open wounds or membranes in warm-blooded animals. When the eggs hatch, the larvae burrow deep into the flesh with hook-like mouths, lending the pest its name. While they most frequently land on livestock and wild animals, they can also infest pets like cats and dogs, and even humans. Victims can develop large open wounds covered in maggots.

It’s treatable. But the rub for ranchers is that if screwworm reestablishes itself in the US, they’ll have to closely inspect their herds – a major challenge in Texas, where ranches can spread across hundreds of acres and labor is scarce. Sick cattle tend to hide away in brush, requiring fine-toothed surveillance to locate and treat them.

An outbreak could cost Texas cattle producers $732 million and deal a $1.8 billion blow to the state economy, according to the US Department of Agriculture. Texas, with its famous history of cattle drives and cattlemen, still has a bigger herd than any other state, with 12.1 million head — about 14% of total US inventory.

The screwworm is likely to be a priority for years even if it never infests an American cow, said T.R. Lansford, the deputy executive director of the Texas Animal Health Commission. That’s partly because of the ban on imports from Mexico, a key source of feeder cattle, which have been mostly blocked since late 2024.

The ban began when Mexican inspectors detected screwworm in a cow at an inspection checkpoint close to the country’s border with Guatemala. Fears intensified in December 2025, when authorities detected the parasite in a six-day old calf in Tamaulipas, a Mexican state bordering Texas.

That case “perks up my cowboy logic,” said Texas Agriculture Commissioner Sid Miller.

The calf was probably too young to have been shipped from farther south, raising the likelihood that it had been infested by an adult screwworm in Tamaulipas. As of Jan. 29, the USDA reported 20 cases in Tamaulipas, including eight that were still active.

If it took decades to push the screwworm out, it took less than five years for the bug to make a comeback.

“This was so effective, I never thought I would be working on screwworm,” said Phillip Kaufman, head of the Department of Entomology at Texas A&M University.

The best way to kill screwworms hasn’t significantly changed since the 1960s. Scientists use radioactive carbon to sterilize screwworm flies, which they release over infested areas. The sterile males then mate with females, who only reproduce once in a lifetime. Over time, populations dwindle. Repeated releases keep resurgences at bay.

Last week, as cases continued to spread in Tamaulipas, the USDA began releasing some sterile flies along the state’s border with Texas.

But full-scale eradication requires a fly-production capacity the US has lost and can’t rebuild for years, even according to optimistic estimates. The eradication campaign required facilities that could produce 500 million sterile flies each week. Currently, global production is concentrated at a single facility in Panama that maxes out at 100 million.

In 1977, the USDA moved its screwworm research facility from an old air base in southern Texas to Mexico. Then, when the US and Mexico dissolved their joint screwworm commission in 2012, the US handed over that facility to the Mexican government, which shut it down soon as the threat waned.

The international effort to eradicate screwworm eventually pushed the pest to the Darien Gap, an inhospitable stretch of jungle on the Panama-Colombia border. But a combination of manufacturing disruptions during the pandemic at the sterile fly facility in Panama and changing grazing patterns are thought to have contributed to the new outbreak.

Officials are now working to rebuild production capacity in North America, leading with a $750 million investment in restarting the Texas air base facility.

The USDA hopes to produce 100 million sterile flies there per week by the spring of 2027, and 300 million by 2029, officials told Texas legislators at a hearing in December. The US also gave Mexico $21 million to help retrofit a fruit-fly facility near the Guatemalan border to produce screwworms as soon as summer 2026.

“We desperately need those flies,” Kaufman said.

Many Texas ranchers are also worried about the threat to wildlife such as deer and feral hogs, which can fuel revenue streams through hunting leases.

There’s already evidence of what would happen to wild animals if the screwworm makes a comeback. In 2016, biologists detected the flies in the Florida Keys, where they infested an endangered species of white-tailed deer. It took five months to push the screwworm out of the state, but in that short time, 15% of the Key deer population died.

“My biggest concern is how it will negatively impact the economics of rural America,” said Donnell Brown, a fifth-generation Texas cattleman at R.A. Brown Ranch in Throckmorton, a spread of 5,000 acres (2,020 hectares) about 160 miles west of Dallas.

Brown never worked on an infested cow. But he remembers the “rancid” tubes of white paste his father kept around to treat them. The odor was so bad, “there’s not even words to describe.”

Now he’s worried the screwworm’s return is imminent.

“My job is to take care of these animals,” he said as he watched a mother cow licking her newborn calf. “I am very concerned that it’s not if, but when.”