‘Horrific’ Flesh-Eating Parasite Headed to U.S.

A “horrific” flesh-eating parasite is headed to the U.S. — and the only way to stop them is by dropping millions of flies on impacted areas.

The New World screwworm is actually a fly — and it is migrating north from South America. It’s been detected less than 400 miles from the Texas border, according to the New York Times.

It’s a “flesh-eating parasite,” Colin Woodall, CEO of the National Cattlemen’s Beef Association, told NPR. As he explained, the fly lays its eggs on livestock, like cattle. Then, he says, “the larva does exactly what the name would suggest. It screws or bores into the flesh of our cattle and, in essence, eats the animal from the inside out. It is a horrific parasite.”

And while it primarily affects animals, the U.S. Centers for Disease Control says it can, and does occasionally sicken humans. The screwworm will lay eggs on an open wound; the CDC cautions that a screwworm infestation is very painful, and “you may see maggots (larvae) around or in an open wound. They could also be in your nose, eyes, or mouth.”

It can cause painful, bloody sores and skin lesions. Perhaps the most vile symptom, per the CDC, is “feeling larvae movement within a skin wound or sore, nose, mouth, or eyes.”

It can kill a cow within two weeks, NYT says, adding there is no approved treatment.

There is, however, a way to stop the flies from reproducing — and as NPR explains, it involves dropping millions of flies on the areas where the parasite has taken hold. 

Entomologist Edwin Burgess explained that they can expose the flies to radiation, which sterilizes them. Then, “They take just the males, and then they package them up and fly them over large areas and drop these little packets out of planes. And then those adult male flies mate with the females.”

The female screwworm fly mates once in her life, so as Burgess says, “if a female mates with a sterile male, she cannot fertilize her eggs, and so she cannot contribute to the population. Eventually, you crash the population of the fly.”

The strategy, called the sterile insect technique, was used in the 1960s, which is the last time the United States saw an infestation of the screwworm. Back then, 600 million sterile flies were released each week, the NYT explains, and the fly was eliminated.

But experts tell the NYT that the U.S. is not ready for the impending screwworm invasion, which is estimated to come within four months.

“We are desperately short on sterile fly production,” Stephen Diebel, vice president of the Texas and Southwestern Cattle Raisers Association, told the outlet. “If we wait, we lose.”

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