A small brown horse with a skin disease on its back
Unlike the maggots of other fly species, screwworms eat living flesh, enlarging even small wounds and potentially killing the animal. Photo courtesy of Animal and Plant Health Inspection Service, United States Department of Agriculture.

Heather Kolich, ANR Agent, UGA Extension Forsyth County

Flesh-eating worms

Late last month, USDA’s National Veterinary Services confirmed that New World Screwworms are back in the United States. Screwworms are the larva, or maggots, of Cochliomyia hominivorax flies. While the maggots of other fly species provide an environmental cleaning service by feeding on dead and decaying animals, screwworms are unique because they eat living flesh.

Female screwworm flies seek out wounds on warm-blooded animals and lay their eggs in them. Even a wound as small as a tick bite may attract screwworm flies; the umbilicus of a newborn calf or fawn provides a rich environment for screwworm eggs. Within 24 hours, 100-300 screwworm eggs laid around the edges of the wound hatch and the maggots begin feeding. They continue feeding for 1-2 weeks as they develop, enlarging the wound as they grow into a potentially fatal lesion.

From the 1930s through the 1960s, screwworms caused economic losses to cattle operations and claimed over 60 percent of white-tail deer fawns each year. U.S. cattlemen led an eradication program that successfully eliminated screwworms from the southeastern states in 1959, and from all areas north of Panama by the mid-1980s. Unfortunately, in late September, screwworm infested deer and other animals were found on Big Pine Key in south Florida.

While Florida may seem far away, adult screwworms fly, and insects can be transported long distances through human movement. The USDA and the University of Georgia are encouraging all livestock and pet owners to closely monitor their animals, and hunters should inspect harvested game for the presence of maggots on fresh kills.

Please collect all suspicious maggots in a sealable container, such as a zip-top plastic bag or a screw-top jar, rather than simply scraping them off the animal onto the ground where they may survive to reproduce. As soon as possible, add isopropyl (rubbing) alcohol to the container to preserve the specimens, and take it to your local Extension office so that the maggots can be identified.

If caught early enough, veterinary treatment can restore infested livestock and pets to full health. Early identification and quick response can help prevent the re-establishment of screwworms in Georgia.

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