Flesh-eating screwworm has reached the US — a comeback driven by organized crime
When the U.S. Department of Agriculture reported this last week detected Ecologist Jeremy Radachowsky wasn’t surprised to find a case of New World screwworm in a calf in Texas.
Radachowsky, Central America and Western Caribbean director of the Wildlife Conservation Society, has long warned about the resurgence of the screwworm fly: a life cycle looks like this plot “Foreign.”
Screwworms incubate only in the wounds or holes of warm-blooded animals such as cows, dogs, horses and humans. The parasite was previously eradicated in North and Central America in a multimillion-dollar effort that spanned decades. fly sterilization program Led by the USA.
But Radachowsky and other researchers I warned you for years Illegal cattle smuggling has accelerated the screwworm’s return to its abandoned territory in Central America, he said. It has since spread north to Mexico and Texas, and as of this week new mexico.
Cattle graze in the Maya Biosphere Reserve in Guatemala; This area is a protected area that should not be grazed by law. – Wildlife Conservation Society
Cattle trafficking is a long-standing problem in Central America; Here, organized crime groups smuggle livestock across borders, some carrying screwworms, without legal health screenings. 2022 report From the think tank InSight Crime.
The report notes that cattle smuggling is lucrative in itself; but it also allows criminal groups to launder money through smuggled cattle and control territory through the deforestation of forests to make way for massive cattle farms.
The influx of cattle and their traffickers into Central American forests has serious consequences, including reduced tree cover, increased violence and the spread of new diseases, Radachowsky said.
Cattle farming often leads to deforestation, as seen here in Guatemala. – Wildlife Conservation Society
“Any cow that is illegally transported has the potential to carry screwworms and other diseases,” Radachowsky said. “One thing that is really scary is that you can catch bird flu and tuberculosis, which are transmitted from cattle.”
USDA and Mexican Ministry of Agriculture They announced new efforts to raise and release sterilized flies to prevent the spread of screwworm. The last time the screwworm entered Texas in the 1970s, epidemic hundreds of millions of dollars in cattle losses.
But Radachowsky warns that unless screwworms are stopped at the source, the problem will persist.
“What we really need is for the governments of the United States, Mexico and (Central American countries) to come together and take significant action to stop this illegal activity, things only they can do,” he said.
Until then, screwworm threatens cost billions of dollars in damage to the beef industry in the southwestern United States.
blame game
Texas Agriculture Commissioner Sid Miller criticized the U.S. response to screwworm and demanded that USDA begin using the Screwworm Adult Suppression System (SWASS), a type of pesticide and bait in addition to sterile fly release.
“I have been pressing USDA for over a year to bring SWASS back into the fray,” Miller said in a statement Monday. He added that he briefed Agriculture Minister Brooke Rollins on the technique “on three separate occasions because we know this tool works.”
Miller even did it last week a personal defense That US President Donald Trump directed USDA to implement the pest management tool.
USDA pushed back In response to Miller’s allegations, the Department’s screwworm task force wrote on social media that SWASS used carcinogenic chemicals and “will also attract and kill the sterile flies we disperse.” At a press conference Monday, USDA Undersecretary Scott Hutchins said the technique was environmentally problematic and “it’s really not appropriate for use anymore.”
There’s plenty of blame to go around. Rollins criticized the Mexican government for “failing to take action against cartel smuggling and immigration and allowing the pest to spread rapidly into southern Mexico.”
Mexican President Claudia Sheinbaum’s office declined to comment when reached by CNN.
While there are experts recommended this recently wave of immigration It is not a disease that can be transmitted from person to person, although animals that carry screwworms may be involved through the Darien Gap in southern Panama.
USDA closed southern border ports to livestock from Mexico in July 2025 to prevent contamination. Rollins said the controversial closure prevented the screwworm from crossing the border sooner.
“We disagree with this measure,” Sheinbaum said when the closure was announced. “The Mexican government has been working on all fronts from the moment we were first alerted to the screwworm.”
Shortly after the United States discovered its first case of screwworm in Mexico closed The border with American livestock farming.
A technician spreads sterilized screwworm flies for release as part of the Mexican government’s fight to stop the spread of the New World Screwworm, which poses a threat to livestock and has led the United States to halt imports of livestock from Mexico on October 17, 2025 in Metapa de Domínguez, Mexico. -Fernando Llano/AP/File
At the call of farmers, Mexico has launched several attacks and raids on its southern border to stop the flow of illegal cattle. However, the screwworm continued its march north.
Sheinbaum acknowledged to reporters last year that “it is sometimes difficult to control the movement of cattle from Central America into our country.”
Meanwhile, Mexican farmers are struggling with screwworms. In September 2025, a farmer in Chiapas, near the Guatemala border, complained about the difficulty of protecting his calves from pests.
“They get the worms within two or three days after birth, and that complicates things because we have to come and keep treating them,” Fidel Gutíerrez said. He told CNN at the time that he had lost a cow to screwworm the previous summer, costing his small farm over $1,000.
Not just cows
Screwworm was once a nuisance to farmers in the southern and southwestern United States. It earned its scientific name, Cochliomyia hominivorax, French naval surgeon Charles Coquerel, whose name means “man-eater” in Latin I came across an example From Devil’s Island in French Guiana, where flies often lay hundreds of eggs in the noses of innocent prisoners.
“Science unfortunately finds itself almost powerless to stop these terrible devastations,” Coquerel lamented in his original report.
A century later Coquerel’s complaint met with an answer. American entomologists Edward F. Knipling and Raymond Bushland found that bombarding New World screwworm pupae with gamma rays would render the males sterile. The duo theorized that populating the wild with irradiated, impotent flies could wipe out the species entirely.
After several trials in Florida, a 1954 experiment on the Caribbean island of Curaçao succeeded in eradicating the screwworm in seven weeks. consecutive releases Collection of sterile flies in the United States by the USDA over the next decade first succeeded in eradicating the screwworm in the United States in 1966. Mexico and other countries in Latin America soon joined the fight against the screwworm, and Mexico eliminated it in 1991. By 2006, the screwworm was exiled from Panama.
An adult New World screwworm fly seen in this undated photo. -Denise Bonilla/U.S. Department of Agriculture/AP/File
But the fly began making a comeback in 2023, possibly reappearing among animals in Panama during the northward migrant surge.
“Once the screwworm crossed the Darien Pass, it moved quite slowly through Panama and then made its way into Costa Rica,” Radachowsky recalled, referring to the 66 miles of trackless jungle between Colombia and Panama.
Then in 2024, Radachowsky noticed something scary: a screw worm that could travel. six to 12 miles It moved much faster if conditions were right.
“Once it got to Nicaragua, it started moving really quickly through the rest of Central America,” he said. “It was moving perhaps over a thousand kilometers (roughly 621 miles) in two months.”
Radachowsky and other ecologists looked at a map showing places where the screwworm appeared and realized that the species was hitching a ride on the meat of illegally traded cattle: patterns of transmission matched previously known smuggling routes.
It’s not just cattle that brought the fly north. On Monday, USDA said: a dog from southern New Mexico It is the first confirmed case of screwworm in the state. Mexican ecologist Andrés Lira, who has been studying screwworms for years, says the main cause of the spread is dogs.
Lira said, “When you look at the current figures, the first thing you see is cattle and sheep.” “The second is canids. It’s quite common in dogs today.”
The screwworm’s presence among dogs has been exacerbated by limited animal control services in Mexico and other parts of Latin America, Lira said.
“These pets that we don’t take good care of are probably spreading this much more than we realize,” Lira said.
As for solutions, Lira doubts that even with a massive sterilization program, the screwworm could be completely eradicated from South America. After all, it is hemisphere specific. South American farmers have learned to account for the effects of screwworms on livestock.
“We are talking about a very large area,” Lira said. “The fly is native. My impression is that we have to learn to live with it.”
Lira, who is currently in Germany on a fellowship, said he had received calls from European food regulators to prepare a battle plan in case the fly crossed the Atlantic.
“They see what’s happening in America and they’re really worried,” Lira said.
CNN’s Jen Christensen, Valeria Leon and Rocio Muñoz Ledo contributed to this report.
Correction: An earlier version of this article included a photo of a man incorrectly identified as Texas Agriculture Commissioner Sid Miller.
For more CNN news and newsletters, create an account at: CNN.com
