Officials Rush to Save Endangered Deer From Flesh-Eating Screwworms

Florida Keys National Wildlife Refuge biologist Kate Watts feeds a key deer some food laced with an anti-parasitic drug that combats flesh-eating screwworms, before marking it with non-toxic paint to signal it's been dosed. Courtesy of Chris Eggleston

Officials in the Florida Keys have begun feeding an antiparasitic drug to endangered deer to prevent the spread of a flesh-eating fly that threatens their survival.

On September 30, the United States Department of Agriculture's Animal and Plant Health Inspection Service confirmed that the New World screwworm had once again returned to Florida—after being eradicated from the U.S. for more than 30 years. The fly larvae were found infecting a number of endangered deer on the Keys and domestic animals on Big Pine Key, which is on the western end of the island chain. In response, the state declared an "agricultural state of emergency," setting up a quarantine that doesn't allow most animals out of the Keys.

The screwworm fly (Cochliomyia hominivorax) has continued to spread among the endangered deer, which have a total population of only 1,300 to 1,500, says Kate Watts, a biologist with the Florida Keys National Wildlife Refuge. Since the screwworm's return, 102 animals too badly infected to be treated have been euthanized, she says. That's more than 10 percent of the primary population of the key deer (Odocoileus virginianus clavium) that live on Big Pine and nearby No Name Key.

On October 11, federal officials began releasing sterilized male flies on Big Pine and shortly thereafter on No Name. These males will mate with female screwworm flies, who breed only once during their life cycle, and thereafter cannot lay viable eggs. This strategy worked to eradicate the fly from the United States in the 1950s and 1960s, and scientists are confident it will work again, says Phil Kaufman, a veterinary entomologist at the University of Florida.

However, it could take nearly six months to get rid of all the flies, Watts says. On October 18, a coalition of local, state and federal officials, scientists and volunteers began feeding the deer pieces of bread laced with an antiparasitic drug known as doramectin, which kills worms and maggots and is commonly used in cattle, Kaufman says. Chris Eggleston, acting head of the refuge on Big Pine, where the infestation was first identified, says he and his colleagues plan to treat the deer once every seven days.

To keep track of the dosing, officials are spraying the deer with small splotches of non-toxic paint after they are fed. They settled on yellow paint for Tuesday, blue paint for Wednesday and pink for Thursday (October 20). This will make it apparent which deer have been fed, and can be dosed again the following week, Eggleston explains.

It took some trial and error to figure out how to do this effectively. The group is currently using small spray bottles. Using pressurized nozzles is a no-go because the "hissing sound really freaks them out," Eggleston adds.

There are other methods to give the antiparasitic drugs to deer, such as injection. But this isn't easy to do, Watts says, and the deer get very upset when they are handled or captured. Sometimes, the stress of such encounters can actually kill them. So, to reduce the stress involved, and because the deer are already unfortunately habituated to being fed by tourists and locals, officials decided to give them food with a side of medicine. "We're trying to turn that fault into a way to treat them," Watts says.

The New World screwworm is one of the few flies that eats living flesh (when it is in its larval form). Lyle J. Buss, University of Florida

Watts and colleagues are currently training community members to help dose the deer, with the aim of treating nearly 100 percent of the animals on Big Pine and No Name.

They also hope to treat the several hundred key deer that live on less-populated, more-wild nearby isles such as Cudjoe, Summerland and the Torch Keys. Realistically, it will be impossible to treat all of these animals, however, since they are wild, live in dense brush and shun human contact—unlike the more tame animals on Big Pine and No Name, Watts says. For these animals, the group is considering using darts for remote injection of the drug.

Kaufman, who isn't involved in the project, says he's happy that officials are doing everything they can to keep the key deer alive, and he's confident their efforts will be successful. He also says that doramectin is an appropriate and relatively safe drug.

Eggleston adds that infected animals that aren't too far gone will be given an injectable antibiotic, which will help their wounds heal. So far two animals have been treated and released.

Screwworms lay eggs in breaks in the skin and can infect many mammals, including humans. They're also one of the few species that feed on living flesh. Key deer are particularly susceptible this time of the year because it's the prime mating season, Watts notes. The males clash in fights over females, creating wounds that screwworms then lay eggs in, which brings maggots that eat living tissue. So far, all but seven of the euthanized animals have been bucks.

As of October 20, 38 deer had been given the medicine, but Eggleston expects that number to go way up after volunteers are trained and join the fight.