In early June, the U.S. Department of Agriculture (USDA) first reported that the New World screwworm—a fly that lays flesh-eating larvae—was found in a baby calf in Texas. There are now close to two dozen cases in domestic animals in the U.S.—all in Texas, including cattle, a goat, and a dog that was identified in Texas but lives in New Mexico.
Here’s what to know about screwworm and the ongoing clash about how to control it.
The screwworm is actually a parasitic fly named for its larvae, which look like squirmy worms. Female screwworm flies lay eggs in wounds or other exposed tissues, such as the eyes, nose, or anal area, of mammals including livestock, dogs, and, less commonly, humans. Unlike maggots, which feast on dead and decaying material, screwworm larvae feed on the tissue of a living mammal host, then drop into the ground where the adult fly emerges after a week or up to a couple of months later, depending on the temperature and humidity.
USDA programs eradicated screwworm flies in the 1960s, but they popped up again in the U.S. in the 1970s and most recently in 2016, in deer in the Florida Keys.
According to the USDA, screwworm does not generally spread from animal to animal or from animals to people. Infestation requires flies to lay eggs in an animal host. If an infected animal does not get treated with anti-parasitic medicines or antibiotics, the larvae can cause sepsis and rupture blood vessels in the animal, killing it in as little as two weeks. Because animals like livestock are often in close quarters, eggs can potentially transfer from one animal to another, so Infected animals should be isolated from others until their wounds heal.
The USDA says screwworm “is not a food safety issue” and that people cannot be infected by eating the meat of an infested animal.
Yes, pets like dogs and cats are just as vulnerable to screwworm infestations as cows and wildlife.
If your pet has a wound, keep a close eye on h
