New World screwworm – (Cochliomyia hominivorax)

As we entered the Florida Keys, we saw electronic street signs warning us of a “screwworm alert”.  Not knowing anything about screwworms, we did some research.  The following is a compilation of information from various sources, including outreach materials, the Monroe County Tourist Development Council, the Florida Department of Agriculture and Consumer Services, the Georgia Department of Agriculture, and the Miami Herald.

New World screwworms are really fly larvae that can infest livestock, pets, and other warm-blooded animals, including people.  A female screwworm fly will lay her eggs – thousands of them – near or on open wounds, the mucous membranes of nose, mouth, or ears, or in the case of newborns, the navel. They feed on the animal’s living flesh. If not treated, infestations are usually fatal within one to two weeks.

On September 30, 2016, New World Screwworm was found in wild deer and pets in the Florida Keys.  132 of the endangered Key deer (see blog entry March 8), mostly males injured during rutting, died by mid-October.  Still mostly confined to the lower and middle Keys, in early January screwworm was found in a stray dog in Homestead, on the FL mainland.  Officials are trying very hard to limit the spread of the fly, establishing a checkpoint with mandatory inspection of all pets and livestock at the northern end of the Keys.

To eradicate the fly, officials are using a biological control called the sterile insect technique. Infertile male flies are released in infested areas. When they mate with local females, no offspring result.  What makes this work is the fact that the female fly typically mates only once in her lifetime. USDA began using this technique in Florida in 1957 and eradicated the flies from the entire southeastern United States by 1959. By 1966, self-sustaining screwworm populations were eliminated from the United States.  After 1982, there were no more re-infestations in the United States, and Mexico was officially declared free of screwworms in 1991.

A joint FDACS and USDA response has been releasing approximately 3 million sterile male flies, twice a week on 9 Keys. Today, the outbreak seems to be diminishing.