Screwworm Eradication: An Interactive View

The parasitic New World screwworm has an interesting history in the United States, and the USDA has developed a series of interactive graphics to illustrate past and present eradication efforts.

The screwworm flies, whose larvae burrow into livestock and other animals causing extensive damage and death, caused substantial losses across the southern United States before eradication efforts began in the late 1950s. Those efforts involved the first use of the sterile-insect technique, a biological-control method that proved very successful. The system uses radiation to sterilize large numbers of male flies, which are then released to mate (unsuccessfully) with wild female flies. With repeated releases of sterile flies, breeding success eventually drops to zero. Over the past 60 years, screwworms have been pushed out of the United States, then Mexico and Central America.

Last fall though, screwworm flies turned up in the Florida Keys, infesting local populations of Key deer, a rare, diminutive subspecies of whitetail deer. Soon after, the parasite was confirmed on the mainland of Florida, infesting a stray dog near Homestead, in Miami-Dade County.

Since then, USDA, Florida State Department of Agriculture and Consumer Services and U.S. Fish and Wildlife Service have undertaken an aggressive eradication effort against the pest to protect livestock and humans, as well as save the Key deer population. The agencies have been releasing about 3 million sterile flies twice each week in the Keys and the Homestead area. In some locations, officials also have used oral ivermectin treatments to protect key deer. Officials expect the eradication effort to take four to six months.

The USDA interactive website illustrates the biology of the screwworm fly and uses maps to illustrate past and present eradication efforts.