There's a new pamphlet on the checkout counter of the ranchers' union supply depot in Hermosillo, Sonora.
On its cover is an image that could just as well be on a campy horror movie poster: a New World screwworm maggot bares its signature "mouth hooks" — which look like little black fangs — that it uses to burrow into living animal tissue.
As ranchers in white cowboy hats sidle up to the counter to order supplies for their sprawling properties south of the Arizona border, the image of the screwworm seems to consider them unseeingly above the Mexican agriculture ministry logo.
"If you lose the trust, the collaboration with ranchers? You're dead. That's the most precious element of this," Julio Berdergué, who led that department from 2024 until May of this year, told KJZZ at a recent event in Washington, D.C.
As the parasite has crept up from Mexico's border with Guatemala over the past year and a half, the Mexican government has been trying to reach out to ranchers across the country. It's provided many with kits they can use to collect samples of possible screwworm maggots and send them in for testing and with medicine to treat open wounds.
Now, the parasite has made its way past the U.S.-Mexico border, with cases in Texas topping 30 since early June when it was first confirmed there.
After well over a year of fighting the parasite, Mexico now could provide lessons to the United States as it deals with an outbreak of its own.
The two countries will also have to work together as they seek to once again eradicate the New World screwworm, said U.S. Department of Agriculture Under Secretary of Marketing & Regulatory Programs Dudley Hoskins.
"Mexico is a critical partner in all this with us," Hoskins said.
If left untreated, the parasite can be deadly. Screwworm flies lay their eggs in the open wounds of warm-blooded animals, and their maggots then feed on the hosts' flesh. The New World screwworm only infects living animals, so meat — and the existing food supply — isn't at risk.
But screwworm spread could raise beef prices from already sky-high levels. Screwworm's arrival in the U.S. comes as the country's cattle herd reaches a 75-year low, even as demand for beef in the United States remains strong.
The average price of a pound of ground beef has risen from under $4 at the start of 2020 to nearly $7 this past April, according to the U.S. Bureau of Labor Statistics.
Vigilance in Sonora
So far, there have been no confirmed cases of New World screwworm in Sonora, where cattle ranching is big business and carne asada tacos reign supreme.
The parasite has appeared in other Mexican states that border the United States. But Sonora "has taken the necessary measures to avoid the arrival of that type of problem here," said Victor Lezama, the veterinarian who runs the ranching cooperative supply store in Hermosillo.
Sonora has rigorous inspections of incoming cattle from other Mexican states, Lezama said. That oversight has kept the movement of animals that has caused the screwworm to spread elsewhere from encroaching upon Sonora, the state's ranching industry says.
Many in Mexico and the United States have pointed to that movement of cattle as one of the main ways the parasite has spread from the far south to the far north of Mexico over the course of the last year and a half.
"It's people that moved animals in Mexico that either were unaware that they were infested or didn't have treatments that were effective when they moved those animals," said Phillip Kaufman, head of the Department of Entomology at Texas A&M University. "That's one of the reasons it moved up Mexico fairly quickly."
Ranchers in the United States, and especially Texas, now need to be checking their cattle for wounds and signs of screwworm more often, especially before they move them, said Kaufman.
The U.S. government is now attempting to reach out to ranchers and spread awareness about the importance of checking their animals, said Hoskins with USDA, much like Mexico's campaigns.
"It will require vigilance and perseverance and awareness day in and day out," Hoskins said. "That will be a new posture that the producer community will have to stand up in response to screwworm."
As the two countries' agriculture departments reach out to ranchers and ask for their help in preventing the screwworm from spreading further, both governments are also in close contact with each other as they try to beat back the parasite, Hoskins said.
Sterile fly program
The United States formally eradicated New World screwworm in the 1960s by releasing sterile male flies into the environment. Those sterile flies mate with normal screwworm flies to dwindle the population — and it remains what most experts consider the most effective tool against the parasite.
But in decades since, the sterile fly program ramped down. Until this summer, a USDA facility in Panama was the only one producing sterile flies. That facility produces approximately 100 million sterile flies per week, which are then dispersed through Mexico and into the United States. Experts warn many more flies will be needed to fully eradicate the parasite and re-confine it to its previous boundary to the south of Panama.
"We don't want very many more of these infestation zones, or it's really going to stress the supplies that we have," Kaufman said.
The United States and Mexico are now rushing to produce more flies. A production facility is under construction in south Texas but is not set to start producing flies until late next year. USDA projects that facility will be able to produce 300 million sterile flies each week.
Late last month, Mexico and the United States together inaugurated a production plant in southern Mexico that USDA says will produce an additional 60 million to 100 million sterile flies per week.
Collaboration between their two countries is part of what Berdegué and Hoskins say prevented the screwworm from arriving in the United States sooner.
"Last summer, all sorts of predictions were that we would have screwworm in Texas by the end of the summer," Kaufman said. "That never happened."
A border still closed
Back in Sonora, rancher Horacio Gamez Lopez waits at the rancher's union headquarters for a meeting with the union president.
A now yearlong border closure for Mexican livestock to protect the United States from screwworm has meant prices on cattle here have plummeted, ranchers say, since so much more cattle now stays in Sonora as exports have halted.
That's had a "drastic" impact on his business, Gamez Lopez said.
"That affects you because you're planning what you're doing on your ranch," Gamez Lopez said. "From one moment to the next they tell you your cattle is worth 42% less, that affects you a lot."
Ranchers like Gamez Lopez say it's not fair that the stretch of border between Sonora and Arizona has remained closed, even though there have been no screwworm cases here.
The USDA is constantly evaluating to decide when it's safe to reopen the U.S.-Mexico border to livestock, Hoskins said.
Gamez Lopez is hopeful that the United States and Mexico will figure out how to eradicate the parasite again together — so the industry here can get back to normal soon.
Copyright 2026 KJZZ News