Texas ranchers brace for return of flesh-eating screwworm
Rising cases in Mexico fuel fears of US livestock outbreak
19 August 2025
3 minute read
By: He was only eight years old in 1973, but fifth-generation Texas rancher Kip Dove remembers spending countless days trotting up to sick and dying cattle on horseback that year during the last major outbreak of flesh-eating screwworm. He carried a bottle of foul-smelling, tar-like medicine in his saddlebag and a holstered revolver to shoot any animals too far gone to treat, according to a recent report from Reuters.
Surrounded by baying cattle dogs and cowboys, the infested cattle kicked and bit at their open wounds, staring wild-eyed at the truck headlights illuminating them and giving off the unmistakable smell of rotting flesh, he recalls.
Now surrounded by a healthy herd of longhorn cattle, Dove is anticipating the return of screwworm, the parasitic fly that eats livestock and wildlife alive. From 1972 to 1976, a screwworm outbreak in the United States infested tens of thousands of cattle across six states, cost tens of millions of dollars to contain, and was only defeated after a massive eradication effort.
Today, the parasitic flies are pushing northward from Central America again after being officially eradicated from the US in 1966, threatening $1.8 billion in damage to Texas’ economy alone, according to a US Department of Agriculture estimate. An outbreak could further elevate record-high beef prices by keeping more calves out of the US cattle supply.
Ranchers in central Mexico are discovering the dreaded fly’s maggots burrowed in their cattle for the first time in a generation, and a factory in Panama is losing a race against time to breed sterile flies, the most powerful tool to quell an outbreak. As cases in livestock – and occasionally in humans and house pets – increase, it's more likely than not that the fly will infest the US again, Dr. Thomas Lansford, assistant state veterinarian at the Texas Animal Health Commission, and other experts told Reuters.
“I don’t know what we’re going to do,” Dove said, folding his arms, scarred from decades of riding horses and chasing cattle through thorny brush.
Female screwworm flies lay hundreds of eggs in wounds on any warm-blooded animal. Once the eggs hatch, the larvae use their sharp, hooked mouths to burrow through living flesh — feeding, enlarging the wound and eventually killing their host if left untreated. A tiny scrape, a recent brand or a healing ear tag can quickly become a gaping wound, carpeted with wriggling maggots.
“The smell is bad, and some of the wounds are horrific. You have humongous holes in these animals teeming with worms,” Dove said. “I don’t know if I could handle it if it happens now."
Washington has halted cattle imports from Mexico and invested millions in setting up a new sterile fly production plant in Metapa, Mexico. But it will take roughly a year to come online. So, cattle producers in the US are stockpiling insecticides, making contingency plans and sounding the alarm that a shortage of skilled ranch labor will hamstring their ability to detect and treat screwworms.
Treatment is low-tech and onerous: vets and ranchers must scrape each worm out of the infested animals by hand before spraying the wounds with an insecticide.
In 1973, Dove was a child who could rope cattle for treatment until 2 a.m. and head to school the next morning. Now at age 60, injuries accumulated from years of ranching would make it more difficult to do the exhausting work of managing cattle during an outbreak, he said.
