What to know about the outbreak of flesh-eating flies in Texas

When U.S. Department of Agriculture officials received news of a Texas calf with a suspicious-looking wound around its umbilical area, what they saw wasn’t an infection—it was an infestation. Maggots weren’t only crawling around the wound, they were eating the three-week-old calf’s healthy tissue, too. It was a tell-tale sign that the New World screwworm was back in the United States, an insect originally eradicated from the country six decades ago.

Officials from multiple countries have been fighting screwworm outbreaks in the Americas for decades, using sterile insects to keep the maggots from spreading and push their range down to the Darién Gap in Panama. Twice since 1966, the insects have popped back up in the United States, but the outbreaks were short-lived. In 2022, the insects pushed beyond the Panamanian containment zone and have been slowly making their way up through Central America and Mexico. For screwworm researchers, the new U.S. cases were inevitable.

Contrary to its name, the screwworm is actually a parasitic fly. What sets it apart from all other North American insects is its affinity for laying eggs in healthy tissue. Upon hatching, the larvae bore further into an animal's body, leaving a wake of necrotic flesh and the smell of death. 

If the infestation is spotted early, animals can recover with treatment. In the worst cases, the flies consume an animal until it dies. 

Since the first confirmed cattle case in the U.S. on June 3, more screwworm infections have popped up around Texas and New Mexico. “It should be expected that things are going to get worse before they get better,” says Grace VanHoy, a veterinarian at UC Davis Weill School of Veterinary Medicine. “When we have an outbreak like this, we’re looking at the tip of the iceberg.”

As officials continue to monitor the outbreak, here’s what to know about screwworms and how to mitigate infestation.

(Why the U.S. government breeds and releases billions of flies a year.) 

What animals are at risk for screwworm infections?

All warm-blooded animals are susceptible to a screwworm infestation—including humans. However, during this outbreak, screwworms have been spotted on cattle, a pet dog, and a goat. 

“No mammal is safe from being infested, because the screwworm flies don't discriminate; they're just looking for a warm-blooded animal that's got a wound on which to lay their eggs in,” says Jonathan Cammack, a livestock entomologist at Oklahoma State University. 

“That wound can be something as small as a tick bite, a barbed wire scratch, something that's gone kind of untreated,” Cammack says. “Our animals, whether we're talking about livestock or wildlife, maybe even pets, they're not walking around with Neosporin and band-aids, so it's up to the human side to be able to provide that care for them,” Newborn animals are especially susceptible to infestation because of their still-healing navel. 

How do screwworms spread?

Although a single screwworm may fly a few miles in a day, its journey through Central America and into the U.S. is largely attributable to the movement of the animals in which its larvae grow. “This isn't like a typical disease, like bacteria or a virus or something that's moving from animal to animal or anything like that,” Cammack says.

Since the outbreak in the U.S., the USDA has implemented quarantines, additional surveillance, and movement restrictions for animals within 20 kilometers of infestations.

While screwworms may be spread through the transportation of living animals, the USDA asserts that spread through meat is not a concern. However, the meat industry may still take a hit from the outbreak.

“From a food safety standpoint, no one needs to worry,” VanHoy says. “Food in the U.S. from livestock is extensively inspected, and there will not be an instance where maggots are going to be in your meat. What may change is the cost of our meat, just because of the increased effort, treatment, and surveillance.” 

In addition to releasing sterile flies across Central America and Mexico to curb the spread, the USDA told National Geographic they’ve released 131 million sterile male screwworms into Texas in preparation for an outbreak since early 2026, and they’re not done yet.

“Millions of flies is a large number; we still want millions more,” says Rear Admiral Michael Schmoyer, the director of the USDA’s New World Screwworm Directorate. It’s the same method that initially eradicated the species from the U.S., ended the subsequent smaller outbreaks, and held the population at the Panamanian border for so many years. 

“The females only mate one time, so we're playing a numbers game, releasing millions of sterile males, just hoping you know we have enough to dilute out the natural population,” VanHoy explains. “I think that we should not panic. There's a lot of really strong programs in place, and we know that we've battled this successfully before. We have history on our side.”

For now, the Panamanian facility known as COPEG produces all the sterile flies used to curtail outbreaks, but new facilities, including one in Mexico and one in Texas, could eventually increase the production of sterile flies. 

How are screwworm cases treated?

“This is easily detectable. It is easily treatable,” says Schmoyer.  “Case in point, the first case in the United States, I received pictures of that particular calf yesterday. It's doing great, so it's a great success story. The faster people can tell us things, the faster we can treat this one.”

Pets with growing wounds and the presence of maggots should be brought to veterinarians, who can provide treatment for pets, and for livestock, the USDA has authorized the emergency use of over-the-counter injectable medication.