Screwworms return to Florida

A photo of a screwworm larva

The horror is back. Screwworms are the only insect that eats the healthy flesh of mammals, including man. Screwworm infections can be fatal to humans. The scientific name of the kind found in Florida is Cochliomyia hominivorax. In Latin, hominivorax means man eater.

Update 5/22/2017: The Department of Agriculture believes they’ve eradicated the screwworms from the Florida Keys. About 135 Key Deer were killed leaving a population of around 740. Most of the deer killed were bucks. Since a buck can breed with more than one doe the population should bounce back quickly.

Where are they?

Screwworms were wiped out in the U.S. 35 years ago, but last fall they were found in the Florida Keys. They’ve mainly infected Key Deer. At least 135 have been killed since September. In order to prevent the parasites from spreading, a check point was set up on U.S. 1 at mile 106 , the only road out of the Keys. In spite of efforts by authorities, the flesh eating insects have now been found on the Florida Peninsula.

Early in January of 2017 it was confirmed that a stray dog in Homestead was infected with screwworms. No one knows where the dog has been or how he became infected. Homestead is 15 miles from the Keys and the infected deer live in the middle and lower Keys, even farther from the mainland. Also no one knows how the deer were originally infected.

Life Cycle

Screwworms are maggots that hatch from eggs laid in open wounds or moist parts of mammals. These larva burrow down into healthy flesh. They feed on the host for five to seven days before falling to the ground. They then tunnel into the ground and later emerge as a fly. The screwworm fly finds a favorable place on a mammal to lay her eggs. The eggs hatch in less than a day and start the gruesome cycle again.

A screwworm laying eggs.
A screwworm fly laying eggs

The Eradication Effort

We eradicated screwworms before. In fact we did so all the way down to the border between Panama and Colombia, so we should be able to do it again. The female fly lives for ten to thirty days laying 400 eggs at a time up to nearly 3000 total, but she only mates once. This is the weakness biologists exploit. The weapon is sterile male flies. If she mates with a sterile male, she won’t reproduce. So far 80 million sterile pupae have been released. Most will become sterile males. When one of these mates with a female, she’s taken off the board.

The last time a screwworm was found in the Keys was January 5, 2017. In order to make sure they’re wiped out, sterile males will be released for at least another three months. On January the 13th officials started releasing sterile males around Homestead where the infected dog was found.

How to Report Screwworms

Help stop these deadly parasites. If you think you see an animal infected with screwworms contact the Florida Department of Agriculture and Consumer Services at 1-800-HELP-FLA (1-800-435-7352) or, for non-Florida residents, (850) 410-3800. To report a sick or injured Key deer including a suspected screwworm infestation, call 1-888-404-FWCC (3922) ext. 7 or 1-305-470-6863 ext. 7.

Photos by the U. S. Department of Agriculture.

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