Cameras set up in remote Central American forests have captured widespread infestations of wildlife with the New World screwworm (Cochliomyia hominivorax). This is a warning sign of how the fly could spread in the US, experts say. This was reported by Qazaqyia.kz citing The Guardian.
According to Jeremy Radachowsky, director of the Mesoamerica and Caribbean program at the Wildlife Conservation Society (WCS), the cameras captured jaguars, pumas, tapirs, deer, white-lipped peccaries, and even porcupines with unmistakable wounds from the parasitic fly. Some mammals shared water sources with cattle that were moved across borders without health checks. The fly then spread through wildlife.
"We see infestations in the deepest parts of the interiors of the forest, so now it's become endemic in wildlife, far from the cattle infestations," Radachowsky said.
In the US, screwworm has been detected in 34 animals, most in Texas, with one in New Mexico. So far, they have only been found in livestock and pets, with no wildlife detections in the US.
The US is now dropping 100 million sterile flies in the southwest and Mexico, which may slow the northward movement of the parasitic fly but will not be enough to eradicate it. For that, about 500 million sterile flies would be needed.
"What we lack are sufficient flies in order to start pushing the population back south," said Phillip Kaufman, professor and department head of entomology at Texas A&M University.
Officials are rushing to expand capacity for breeding sterile flies. One facility opened in Mexico in late June 2026, with another in Texas planned for late 2027. These flies are irradiated so they cannot reproduce; when males mate with females, the eggs are not fertilized, crashing the population.
New innovations are on the horizon, such as raising only sterile male flies or designing better bait traps. But these methods take time to develop.
"We have to have things that work. We can't stop doing things we know work in order to try things that don't have any data to support. We are relying on science to solve this problem," Kaufman said.
Radachowsky argued that efforts have focused on the screwworm itself, not the root cause: illegal cattle trafficking.
"They're either eradicating the fly, making a fly that can't reproduce or trying to trap the fly. What they're not doing is addressing the root cause of the cattle trafficking. If you're only using sterile fly technique and you have other factors that are moving beyond your efforts to blanket those areas with sterile flies, you're never going to have the capacity to clear huge areas," he said.
Radachowsky noted that the livestock industry, especially illegal cattle movement, has changed significantly since the flies were pushed out in 1966.
"There's this expectation that the sterile fly technique worked once, so it will work again. But in the 60s, we didn't have this high density of cattle like we do now. The human population and cattle population is just incredibly different, and the illicit cattle movements didn't exist before," he said.
The screwworm got through the Darién Gap in 2022, reaching Nicaragua. From there, "it basically shot northward through Central America," moving thousands of kilometers in only four or five months — "at the speed of a truck, and exactly along those illegal cattle-trafficking routes that we had already documented," Radachowsky said.
Illegally moving animals does seem like the primary driver for the return of the screwworm, Kaufman said.
"There's not a lot of wildlife that go on long-distance migrations in this region. When you see it jump 50 or 100 miles, that wasn't an adult fly flying that far. They don't do that. It was people," he said, transporting livestock or pets.
US Agriculture Secretary Brooke Rollins met with ranchers in Kerrville, Texas, on June 8, 2026, playing a key role in coordinating screwworm response efforts.