RIVERSIDE, Calif. (Border Report) — During the late 1800s and well into the 1900s, the New World screwworm invaded the U.S., devastating livestock and requiring a decades-long eradication campaign.
During that time, the fly could be found from California to Florida.
Eventually, scientists discovered that by releasing sterile male flies into the air, they could all but eliminate the species.
“By 1966, California was one of the last places the fly was eradicated from,” said Alec Gerry, a professor of veterinary entomology at the University of California Riverside.
Gerry and other researchers at the school are working to prevent the fly’s threatened return to California and other states such as Texas.
“By the 1990s they had actually driven the population all the way south of Panama. Unfortunately, in 2023, the flies escaped northward of that barrier zone and have been moving north through Central America and up into Mexico creating concern the flies might once again reach the U.S.”
Earlier this year, the New World screwworm was found 70 miles south of Texas, prompting the U.S. Department of Agriculture to stop all imports of Mexican cattle.
This screwworm isn’t a worm at all; it’s the larval or the maggot stage of a shiny, metallic blowfly, a species called Cochliomyia hominivorax.
While many blowflies are harmless and play a vital role in decomposing dead animals, this particular species feeds on living flesh, Gerry said.
The screwworm is known for laying its eggs in open wounds on warm-blooded animals, including humans.
The maggots burrow into flesh in a corkscrew motion in a process that gives the fly its name.
“They actually eat the living tissue of those animals, enlarging the wounds and oftentimes resulting in the death of the animal,” Gerry said. “The adult flies can fly, but the immatures, the maggots if you will, are found in open-flesh wounds and are often moved with the animal, so if you move animals from one location and they’re infested with these maggots already and you don’t realize it, you move the flies to another location.”
Gerry says he and fellow scientists at UC Riverside are gearing up to begin surveillance programs looking for the flies in California.
They will also be working with the U.S. Department of Agriculture to update education and pest management materials aimed at the public that haven’t been upgraded in 60 years.
The California Department of Food and Agriculture is providing more than half a million dollars in funding to UCR to perform the work.