Screwworm Returns To The United States


The screwworm eradication program—a triumph of animal health science—came with unintended consequences.

When the flesh-eating pest was eradicated and big predators were removed, deer numbers exploded. Now more than ever we need to protect deer predators for the health of the deer herds and their habitat, which cattle share with wildlife.

NOTE: This post initially appeared on on October 23, 2016

Screwworms, which feast on live flesh, found in S. Florida

If pythons and crocodiles weren’t enough, a new troublesome creature has taken up residence in South Florida — the screwworm.

Gory photos of screwworms eating wild deer alive have made the rounds on the internet, turning stomachs and stoking fears that the insect might spread beyond Florida and harm livestock in Texas and other states.

While screwworms once were a scourge to cattle in Texas, the odds of them turning up again in the Lone Star State seem remote for now. Many decades ago, the worms were responsible for killing thousands of cattle in this state.

The current infestation has been confined to a small population of endangered deer that live on one of Florida’s remote southern Keys, which has enabled wildlife officials to establish an effective blockade.

Also, Florida officials are using an eradication method that has had a proven track record. It involves releasing sterile male screwworm flies, which mate with females that then lay infertile eggs.

Still, it’s understandable why federal and state agriculture officials are on alert for the pest, which was last seen in the United States in 1982.

Screwworms caused devastating livestock losses up until the early 1950s, when scientists discovered that releasing sterile male flies would stop the spread of screwworms. For example, in 1935, Texas counties reported more than 180,000 livestock deaths because of screwworms.

What makes screwworms so unique — and deadly — is that they feast on live animal flesh, unlike other blowflies that consume carrion, or rotting meat. Female screwworm flies are attracted to open wounds and lay hundreds of eggs inside them. Then the larvae hatch and begin eating their host alive.

“It’s definitely not something you want to Google,” Sonja Swiger, a Texas A&M entomologist based in Stephenville, said of pictures of animals with screwworm infestations.

Swiger said that while there’s no reason to worry about screwworms in Texas, ranchers should familiarize themselves with the pest, which is hard to miss, given its habits.

“Think about it. If screwworms returned, it could be the end of part-time ranching,” Swiger said. “Except for the dead of winter, stockmen would have to constantly watch their stock for wormies. And white-tailed deer, which give birth in warm weather, and bucks in velvet with blood-engorged antlers, I expect would be easy targets as well.”

Ranching, wildlife management, finance, oil & gas, real estate development and management.

Leave a Reply

Your email address will not be published. Required fields are marked *