Swarm and awe: US to use flies vs a pest
TOPEKA, Kansas—The US government is preparing to breed billions of flies and dump them out of airplanes over Mexico and southern Texas to fight a flesh-eating maggot.
That sounds like the plot of a horror movie, but it is part of the government’s plans to protect the United States from a bug that could devastate its beef industry, decimate wildlife, and even kill household pets. This weird science has worked well before.
“It’s an exceptionally good technology,” said Edwin Burgess, an assistant professor at the University of Florida who studies parasites in animals, particularly livestock. “It’s an all-time great in terms of translating science to solve some kind of large problem.”
The targeted pest is the flesh-eating larva of the New World Screwworm fly. The US Department of Agriculture plans to ramp up the breeding and distribution of adult male flies—sterilizing them with radiation before releasing them—so they can mate ineffectively with females and over time cause the population to die out.
It is more effective and environmentally friendly than spraying the pest into oblivion, and it is how the United States and other nations north of Panama eradicated the same pest decades ago. Sterile flies from a factory in Panama kept the flies contained there for years, but the pest appeared in southern Mexico late last year.
The USDA expects a new screwworm fly factory to be up and running in southern Mexico by July 2026. It plans to open a fly distribution center in southern Texas by the end of the year so that it can import and distribute flies from Panama if necessary.
Serious threat
Most fly larvae feed on dead flesh, making the New World screwworm fly and its Old World counterpart in Asia and Africa outliers—and for the American beef industry, a serious threat. Females lay their eggs in wounds and, sometimes, exposed mucus.
“A thousand-pound bovine can be dead from this in two weeks,” said Michael Bailey, president-elect of the American Veterinary Medicine Association.
Veterinarians have effective treatments for infested animals, but an infestation can still be unpleasant—and cripple an animal with pain.
Don Hineman, a retired western Kansas rancher, recalled infected cattle as a youngster on his family’s farm.
“It smelled nasty,” he said. “Like rotting meat.”
The New World screwworm fly is a tropical species, unable to survive Midwestern or Great Plains winters, so it was a seasonal scourge. Still, the United States and Mexico bred and released more than 94 billion sterile flies from 1962 through 1975 to eradicate the pest, according to the USDA.
The numbers need to be large enough that females in the wild can’t help but hook up with sterile males for mating.
Alarmed about the fly’s migration north, the United States temporarily closed its southern border in May to imports of live cattle, horses and bison, and it won’t be fully open again at least until mid-September.
