Screwworm Outbreak Threatens Pets in Florida Keys

Posted by Stacey Venzel
dog scratching itself on beach

Flesh-eating larvae are attacking endangered animals in the Florida Keys, and the outbreak is spreading to house pets and farm animals.

Better check your pets before you leave or enter the Florida Keys. A parasitic infestation in Big Pine Key, Florida has caused over 50 endangered Key deer to be euthanized since the outbreak began a few months ago. The last census reported that only an estimated 1,000 Key deer remain.

But the insects are feasting on more than just deer.

According to the Miami Herald, the larvae have caused a pot-bellied pig and two dogs to be euthanized in Monroe County, a region that spans the uninhabited Everglades into Key Largo and down to Key West, Florida.

blow fly screwworm
Franco Falini/Flickr

Female blowflies lay screwworm eggs in open wounds and sores, in addition to trash bins, road kill, and dung. After hatching, the larvae then burrow deep into the skin, causing lesions. Some populations of blowflies feed only on necrotic tissue, but Keys veterinarian Dr. Doug Mader warns that the New World screwworm eats live tissue.

The U.S. Department of Agriculture has been called in to obliterate the larvae, with an agricultural emergency declared in Monroe County. Infected Key deer are being frozen and cremated to kill the larvae, which makes a host out of warm-blooded animals. Maggots drop off into the soil when they’re done feasting, where they then complete their maturation and regenerate. Cremation and freezing prevents completion of the full life cycle.

Employing a biological population control method called the “sterile insect technique,” sterile male flies are on their way south to mate with viable females, effectively halting reproduction and stopping the spread of infestation. The process has seen successful with screwworm outbreaks in the past.

fly strike screwworm
Lawrence Wright/Flickr

Precautions are being taken throughout the state. The Monroe County Sheriff ‘s Animal Farm was even closed to visitors on Sunday as a safety measure.

Marie Simpson, a resident of Marathon, Florida at the 50-mile marker in the Florida Keys, works at an animal shelter in the city. She has a rescue dog of her own. She said:

“It is concerning for pets! If anyone leaves the Keys with their pets, they are supposed to have them checked at a checkpoint so it doesn’t spread.”

Indeed, a checkpoint was set up at mile-maker 106, the start of the famed 18-mile stretch entrance to this archipelago slice of paradise. The control post, which closed briefly when Hurricane Matthew passed through, is voluntary, however.

Mader, president-emeritus of the North American Veterinary Conference (NAVC), attempted to assuage concerns of Florida Keys pet guardians. He has seen a handful of cases at his practice, most with favorable results.

screwworm dog

Mader does advise area owners to keep wounded pets indoors until the sore has healed so as to not provide flies with breeding grounds. He also urged guardians to seek immediate care if they suspect screwworm, and not to try to remove the maggots themselves. A veterinarian can properly treat the painful disease, report it accordingly, and dispose of the larvae appropriately.

Fly strike spray on farm animal wounds can help prevent barnyard pets from contracting screwworm. Infected pets will need to have the area thoroughly cleaned and follow a course of antibiotics to deter infection.

It has been five decades since screwworm was last seen in the state, and the parasite was thought to have been eliminated from U.S. borders over three decades ago. But vigilant owners can prevent screwworm infestations!


Screwworm Outbreak Threatens Pets in Florida Keys