When the US Department of Agriculture reported final week that it detected a case of New World screwworm in a Texas calf, ecologist Jeremy Radachowsky was not shocked.
Radachowsky, the Mesoamerica and Western Caribbean director for the Wildlife Conservation Society, had lengthy warned of the resurgence of the screwworm fly: a species with a life cycle that appears like the plot of “Alien.”
Screwworms incubate solely in the wounds or orifices of warm-blooded animals equivalent to cows, canine, horses and human beings. The parasite had beforehand been eradicated in North and Central America by way of a multimillion-dollar, decades-long program of fly sterilization led by the United States.
But Radachowsky and different researchers have warned for years that unlawful cattle smuggling has quickened the return of screwworm to its ceded territory in Central America. It has since unfold northward to Mexico, Texas and, as of this week, New Mexico.
Cattle trafficking is a long-standing subject in Central America, the place organized crime teams smuggle livestock, a few of which carry screwworm, throughout borders with out professional well being screenings, in accordance with a 2022 report from the suppose tank InSight Crime.
The report notes that cattle trafficking is profitable by itself, however the phenomenon additionally permits legal teams to launder cash by way of smuggled cattle and management territory through jungle deforestation to make room for large cattle ranches.
The inflow of cattle and their traffickers into the forests of Central America has had severe penalties, Radachowsky mentioned, together with receding tree cowl, rising violence and the unfold of recent ailments.
“Every cow that is being moved illegally has the potential to carry a screwworm and other diseases,” Radachowsky mentioned. “Something that’s really frightening as well is that you have avian flu transmitted by cattle and tuberculosis.”
The USDA and the Mexican Agriculture Department have introduced new efforts in breeding and releasing sterilized flies to hamper the unfold of screwworm. The final time the screwworm wriggled its manner into Texas, in the Nineteen Seventies, the outbreak prompted hundreds of millions of dollars in cattle losses.
But Radachowsky warns that until screwworm is stopped at the supply, the drawback will stay.
“What we really need are the governments of the United States, Mexico and (Central American countries) to come together and take considerable action in things that only they can do, in order to shut down this illicit activity,” he mentioned.
Until then, the screwworm threatens to price billions of dollars in damage to the beef business in the southwestern United States.
Texas Agriculture Commissioner Sid Miller has been a critic of the US response to screwworm, demanding that the USDA start utilizing the Screwworm Adult Suppression System (SWASS), a sort of pesticide and bait, along with sterile fly releases.
“For over a year, I’ve been pushing USDA to bring SWASS back into the fight,” Miller mentioned in a assertion Monday. He added that he has given Agriculture Secretary Brooke Rollins details about the method “three separate times because we know this tool works.”
Miller final week even made a personal plea that US President Donald Trump direct the USDA to deploy the pest administration instrument.
The USDA has pushed back on Miller’s claims, with the Department’s screwworm job power writing on social media that SWASS makes use of carcinogenic chemical compounds and “would also attract and kill the sterile flies we are deploying.” At a Monday press convention, USDA Undersecretary Scott Hutchins mentioned that the method is environmentally problematic and “no longer really viable to utilize anymore.”
There is loads of blame to go round. Rollins has criticized the Mexican authorities for not cracking down on “cartel trafficking and immigration, allowing the pest to spread quickly across southern Mexico.”
Mexican President Claudia Sheinbaum’s workplace declined to remark when reached by NCS.
While specialists have suggested that a current wave of migration by way of the Darien Gap south of Panama could have included animals carrying screwworm, it’s not a illness that may be transmitted from individual to individual.
The USDA closed southern border ports to livestock from Mexico in July 2025 to forestall transmission. Rollins has credited the controversial closure with conserving the screwworm from crossing the border earlier.
“We do not agree with this measure,” Sheinbaum mentioned when the closure was introduced. “The Mexican government has been working on all fronts from the very first moment we were alerted to the screwworm.”
Soon after the US found its first circumstances of screwworm, Mexico closed its border to American livestock.
At the urging of ranchers, Mexico has carried out quite a few stings and raids at the southern border to stanch the move of unlawful cattle. But the screwworm continued its march north.
Sheinbaum acknowledged to reporters final yr that “sometimes it is difficult to control the passage of cattle coming from Central America into our country.”
Mexican farmers have struggled with screwworm in the meantime. In September 2025, one farmer in Chiapas, close to the Guatemala border, bemoaned the problem of conserving his calves protected from the pest.
“They get the worms within two or three days of birth, and that complicates things because we have to come and keep treating them,” Fidel Gutíerrez mentioned. He instructed NCS at the time that he had misplaced one cow to screwworm the summer time earlier than, at a price of over $1,000 for his small farm.
Screwworm was as soon as the bane of ranchers all through the southern and southwestern United States. It earned its scientific title, Cochliomyia hominivorax, Latin for “man-eater,” when Charles Coquerel, a French naval surgeon, encountered a specimen from Devils Island in French Guiana, the place the flies usually laid a whole bunch of eggs in unsuspecting prisoners’ noses.
“Science unfortunately finds itself nearly powerless to halt these terrible ravages,” Coquerel lamented in his authentic report.
A century later, Coquerel’s grievance met a solution. American entomologists Edward F. Knipling and Raymond Bushland discovered that bombarding New World screwworm pupae with gamma rays would render the males sterile. The two theorized that flooding the wild with the irradiated, impotent flies might extinguish the species totally.
After a few trial runs in Florida, an experiment on the Caribbean island of Curaçao in 1954 managed to banish the screwworm in seven weeks. Successive releases of sterile flies by the USDA throughout the United States over the subsequent decade managed to initially eradicate the screwworm in the US in 1966. Mexico and different nations in Latin America joined the conflict on the screwworm quickly afterward, with Mexico eliminating it in 1991. By 2006, the screwworm was banished from Panama.
Yet the fly started to make a comeback in 2023, probably reemerging in Panama amongst animals throughout a migrant surge northward.
“When screwworm broke through the Darien Gap,” Radachowsky recalled, referring to a 66-mile stretch of roadless jungle between Colombia and Panama, “it sort of traveled fairly slowly through Panama and then made its way into Costa Rica.”
Then, in 2024, Radachowsky observed one thing scary: The screwworm, which may journey six to 12 miles if situations are favorable, was shifting at a a lot quicker fee.
“When it got to Nicaragua, it started to move really, really rapidly throughout the rest of Central America,” he mentioned. “It was moving above maybe a thousand kilometers (roughly 621 miles) in two months.”
Radachowsky and different ecologists checked out a map of the place screwworm had appeared and realized that the species was hitching a experience in the flesh of illegally trafficked cattle: the transmission cases matched the path of beforehand identified trafficking routes.
It’s not simply cattle that convey the fly north. On Monday, the USDA mentioned that a dog from southern New Mexico is the state’s first confirmed case of screwworm. Andrés Lira, a Mexican ecologist who has studied the screwworm for years, says that canine are a main driver of the unfold.
“If you look at the current numbers, first it’s cattle and livestock,” mentioned Lira. “Second is canids. It’s highly prevalent in dogs today.”
Lira famous that the screwworm’s presence amongst canine is compounded by restricted animal management companies in Mexico and different components of Latin America.
“These companion animals that we don’t take good care of are probably spreading this much more than we could understand,” Lira mentioned.
As for options, Lira is skeptical that the screwworm may very well be eradicated in South America totally, even with a large sterilization program. It is, in any case, native to this hemisphere. South American farmers have realized to account for the screwworm’s results on their livestock.
“We’re talking about a huge territory,” Lira mentioned. “The fly is native. My impression is that we’ll have to learn to live with this.”
Lira, presently in Germany on a fellowship, mentioned he has already fielded calls from European meals regulators to provide you with a battle plan in case the fly crosses the Atlantic.
“They see what’s happening in the Americas,” Lira mentioned, “and they are really worried.”
NCS’s Jen Christensen, Valeria Leon and Rocio Muñoz Ledo contributed to this report.
Correction: An earlier model of this text included a picture of a man incorrectly recognized as Texas Agriculture Commissioner Sid Miller