The New World screwworm (Cochliomyia hominivorax), a flesh-eating fly that was eradicated from the United States 60 years ago, has reappeared in Texas cattle, according to U.S. Agriculture Department officials. The USDA had confirmed six cases as of Thursday, including four involving South Texas calves.
Texas rancher Stephen Diebel, a fifth-generation cattleman and president of the Texas & Southwestern Cattle Raisers Association, said he spent 18 months tracking the parasitic fly’s advance toward the U.S. border. When it struck his herd last week, he said, he was ready. On his cow-calf operation in Texas’s southeastern plains, Diebel said he is limiting opportunities for the pest by pushing the birthing season for his calves to colder months when flies are less active — a process that can take years, according to ranchers and industry analysts. Diebel also said he uses drones to monitor his cattle for unusual behavior that might signal an infestation.
The fly lays hundreds of eggs in the open wounds or body cavities of warm-blooded animals, in openings as small as a tick bite. The larvae use screwlike spines to burrow into and feed on tissue, often causing an infection that can kill an animal in weeks.
Freddy Nieto, a fourth-generation cattleman on a ranch near the Rio Grande, said he has not yet seen the screwworm himself. His 80-year-old father, Lupe Nieto, is familiar with it. In the 1960s and 1970s, Lupe Nieto would rise before dawn to pack coffee and a camp lunch in one saddlebag and an acrid, tar-like screwworm killer in the other. Cowboys would scrape wriggling larvae from wounds on cattle and smear the now-banned paste over the wound.
“Back then, they had 30 cowboys who rode every day, seven days a week, doctoring cattle. I’ve got five,” Freddy Nieto said. He has lost count of the legal pads he has filled designing his own battle plan.
The younger Nieto’s cowboys can examine each herd only every other day, with equipment operators and fence crews handling some daily chores. The ranch uses drones to monitor cattle; if the outbreak spreads, Nieto expects to hire more employees, adding to operating expenses.
Diebel said a dwindling workforce is among the biggest obstacles to screwworm management. “Certainly we don’t have the labor force that we did back in the ’60s and the ’70s,” he said.
The USDA has estimated that if not contained, the screwworm could saddle Texas ranchers with more than $700 million in losses a year, largely from livestock deaths. The economic impact could be even larger, the agency said.
The parasite has also been detected beyond cattle. The USDA said Monday that a screwworm-larvae infestation was found on a dog in New Mexico.
Livestock are not the only animals at risk. Texas hosts a $9.6 billion white-tailed deer hunting industry that relies on a deer population that has boomed since screwworm’s eradication. John Paul Schuster, a Kinney County judge and rancher, said he and his wife, Donna Schuster, raise cattle and lease part of their property to hunters. “If we start losing our wildlife, that’s a vacuum on my little community, my county,” he said.
The U.S. first eradicated the parasite in the 1960s by releasing sterile screwworm flies over infested areas, eventually pushing the pest beyond the Darién Gap on the Panama-Colombia border. Female flies mate only once, so sterilized males suppress the population. As the risk declined, the U.S. closed most sterile fly production facilities.
The USDA said it now needs about 500 million sterile flies a week to once again eliminate the pest from the U.S. — around five times the output of its only operating facility in Panama. Two more facilities are under construction, including a new $750 million plant in South Texas. Agency officials said ramping up production could take over two years.
Agriculture Secretary Brooke Rollins said the agency was exploring innovations to improve sterile fly production efficiency, including offering $100 million in grants to private-sector partners.
Meanwhile, Freddy Nieto has a plan if screwworm afflicts his cattle. “I guarantee you,” he chuckled, “if we get a case, my dad is the first one I’m sending to go look at it.”