Experts warn of ways screwworm could spread in the US and new difficulties in keeping it at bay

The endemic presence of the new world screwworm in wildlife in Central America and the illegal cattle industry have helped the spread of the parasite. Photograph: Brandon Bell/Getty Images View image in fullscreen The endemic presence of the new world screwworm in wildlife in Central America and the illegal cattle industry have helped the spread of the parasite. Photograph: Brandon Bell/Getty Images Experts warn of ways screwworm could spread in the US and new difficulties in keeping it at bay Scientists worry that current eradication efforts won’t be able to contain parasitic infestation pushing into US When conservationists set up cameras in remote regions of Central American forests, they wanted to monitor illegal cattle movement, which can lead to deforestation . But in recent months, they discovered another alarming development: wildlife rapidly infected with the new world screwworm. It’s a warning sign of how the fly could spread in the US – and it signals new difficulties in pushing it back south, a process that will probably take years, experts say. “We got a really unique perspective throughout the beginning of the process,” said Jeremy Radachowsky, director of the Mesoamerica and Caribbean program at the Wildlife Conservation Society, which recently released a study on the phenomenon. The cameras captured all types of wildlife – jaguar, puma, tapir, deer, white-lipped peccary, even porcupines – covered in the unmistakable wounds caused by the parasitic fly. Some of the mammals shared water sources with the cattle, which were moved across national borders without requisite health and safety checks. From there, the fly ripped 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. View image in fullscreen The Texas operations center during the state’s response to the infestation, in Austin, on 5 June 2026. Photograph: Austin American-Statesman/Hearst Newspapers/Getty Images Screwworm has been detected in 34 animals in the US – 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. Farm workers at higher risk amid screwworm outbreak in US south-west Read more The US is now dropping 100 million sterile flies in the south-west and Mexico – which may be enough to slow the northward movement of the parasitic fly, but will not be enough to eradicate it from the region. For that, they would need about 500 million sterile flies. “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 now rushing to expand the capacity for breeding sterile flies. One facility opened in Mexico in late June, with another facility in Texas planned to open in late 2027. These flies are irradiated so that they cannot reproduce;