Flesh-Eating Screwworms Move Inland In Florida

Screwworms Have Spread Past The Florida Keys

Back in October screwworms made a reappearance after 30 years in the Florida Keys. However, this week the U.S. Department of Agriculture had more bad news, a stray dog near Homestead, Florida- 15 miles north of the Keys- was found with wounds infested with screwworms.

“The screwworm is a potentially devastating animal disease that sends shivers down every rancher’s spine,” said Florida’s Commission of Agriculture Adam Putnam, in a statement that accompanied the official declaration of agricultural emergency last October, obtained by the Atlantic.


The infestation in the Keys was bad, but had been somewhat isolated. After the initial outbreak officials set up an animal health checkpoint on U.S. Highway 1, the main road leading in and out of the keys. There officials would scan animals leaving the keys for infestation with screwworms.

At this point it is not clear how the stray dog got infested or where it had been prior to where it was found in Homestead. A vet in the area notified the USDA and the dog has been treated.

“It’s a very treatable condition if caught early,” says USDA veterinary medical officer Robert Dickens to the Atlantic. “The dog is doing really well.”

What Are Screwworms And How Can You Prevent Them

Screwworms, Cochliomyia hominivorax, are about the same size as common houseflies as adults, but they have orange eyes instead. The parasite lays eggs near open wounds in warm-blooded animals. Unlike most maggots, these larvae hatch and “screw down” into the host organism, feeding on living flesh along the way. After they cause substantial damage, distress and sometimes death to the host animal, the screwworms fall away from their host to pupate and turn into flies.

The flies don’t often fly very far, but infected animals can spread infestations if they move to new areas. Livestock and pets are at the highest risk, though in some rare cases humans can become infected as well.

Photo: Artist view of larval screwworms embedded in would. U.S.D.A. Emporia State Univeristy, Screwworm Eradication.

Symptoms of a screwworm infestation include a festering wound or sore, unexplained lumps under the skin, and an unusual discharge or foul odor.

Back in the mid 1950’s when Florida was experiencing its last outbreak of the parasite, entomologists studying ways to counter the insect found that they could render males sterile through exposure to X-rays. Since female screwworm flies only mate once, releasing millions of sterilized males into the infested areas would relatively break the life cycle. When Florida began this sterilization method in 1958 it took less than one year for screwworms to be completely wiped out in the state.

Agriculture officials announced in October the release of millions of sterilized male screwworm flies. Any eggs produced won’t hatch, eventually killing the fly population over time.

Putnam said in October the releases would continue twice weekly for six months.

Chemical treatments are available for infested cattle and pets, but the sterilized insect release is so effective that pesticides aren’t necessary.