A deadly, flesh-eating parasite has once again invaded southern Florida and is ravaging animals, sparking a local agricultural emergency. State and federal authorities there are now fighting to zap the invasive infestation before it can cause catastrophic damage to the region.

The New World screwworm fly, which infests open wounds and feasts on living tissue, was last seen in the US during the 1970s, following half-a-century of hard-fought eradication efforts in the Southeast US and Central America.

But this year, state officials in the Florida Keys started seeing grotesque lesions on Key deer—an endangered species that is the smallest of North America’s white-tailed deer. Since July, about 15 percent of the Key deer population (132 animals) have died of the infection, and authorities have found other animals in the area, mostly pets, infected. Authorities confirmed the fly’s return through lab testing in late September.

Though the fly larvae can lay waste to any warm-blooded animal, including humans, the parasites are particularly damaging to cattle and other livestock. When the New World screwworm fly last peaked in America during the 1930s, it caused millions of dollars in damages to livestock producers each year. If it regains its hold, the US Department of Agriculture estimates that it could cause more than a billion in damages annually.

How it returned is still a mystery. However, authorities suspect that the fly arrived in migrants, animals, or cargo from Haiti or Cuba, many of which frequently land in the Florida Keys. The fly is native to tropical areas and has continued to pop up in the Caribbean and Central American countries despite eradication efforts.

“In the very big picture, this is just the latest example of our failure to adequately protect people, agriculture and the environment from consequences of a shrinking world, an interconnected word,” Adam Putnam, Florida’s commissioner of agriculture, told The New York Times.

Federal and state authorities have dusted off decades-old eradication strategies, setting up quarantines and check zones for all animals moved through affected areas, feeding anti-parasite medication to deer, and releasing sterile male flies each week. Because female flies only mate once in their lifespan, the millions of sterile males foil breeding by acting as fertility decoys that effectively swat down population growth.

So far, the efforts seem to be working. Last Thursday, the US Fish and Wildlife Service announced that the death toll is currently holding steady, with no new reports of dead deer in over a week. However, the agency notes that it is “remaining diligent with protection measures.”

Managers of the National Key Deer Refuge continue to inspect the tiny critters for the signs of infection—hideous expanding wounds full of squishy, flesh-eating maggots. Those larvae were dubbed screwworms because of the spines along their bodies that resemble the threads of a screw. The adult screwworm flies, on the other hand, are less distinguishable, resembling a common house fly, maybe a little bigger. They lay their eggs on the edge of open wounds, which can be anything from a tiny tick bite to a castration incision or the navel of a newborn. The hatched screwworms then dive headfirst into the wound or opening, munching on living tissue while resembling a screw being driven into tissue.