Screwworms Back In Florida

It’s literally been a few generations ago that we last dealt with screwworms. There has been a reinvasion in South Florida, and an eradication program is underway. UGA Extension Livestock Entomologist Dr. Nancy Hinkle has good information on the current situation.

In late September the USDA’s National Veterinary Services confirmed that New World Screwworms had been found in deer on Big Pine Key in south Florida. Additional screwworm-infested animals have been located in the same area since.

Lifecycle

Screwworms will lay their eggs on any wound in an animal–even an area as small as a tick bite. They are unusual in that the maggots feed only on living flesh (while other types of maggots consume necrotic tissue). Once the maggots have gotten as big as they are going to get, they crawl out of the wound, fall to the ground, burrow into the soil and pupate. A few days later the adult fly will emerge from the pupal case, seek a mate, and start the life cycle all over again.

History

Screwworms were a scourge of the Southeast from the 1930s to the 1960s. Cattlemen funded an eradication program to eliminate screwworms using the sterile insect technique, successfully eliminating screwworms from the Southeast in 1959. They were eradicated from the rest of the U.S. in the 1970s, and by the mid-80s screwworms had been eradicated from all areas north of Panama, where they have been maintained since. South American countries still have thriving screwworm populations, so risk of reintroduction persists.

This is a reportable disease, so veterinarians are being particularly vigilant. Cattlemen can watch their animals to ensure that screwworms do not develop in their herd. Other livestock such as goats, horses, swine, etc. can also be infested by screwworms, so should be checked regularly.

Back in the 1950s screwworms killed over 60% of white-tailed deer fawns born every year. Hunters may want to keep a ziploc bag with them in the field to scoop maggots out of wounds on deer they kill, so they can be submitted for identification.

Identification

Pet-owners should keep an eye on their animals to avoid screwworms infesting their pets. Contact your veterinarian to have any suspicious maggots checked out.

Any suspect maggots should be put into a container of alcohol and submitted to the County Extension office. Don’t just scrape the maggots off on the ground and let them crawl away! We want to eliminate these pests before they have a chance to re-establish in Georgia.

Screwworms can be treated and the animals will recover fully, if the infestation is caught in time.

Again, other types of maggots can be found in wounds, but screwworms are the only maggots that feed on the living tissue and enlarge the wound. Screwworms cannot live in dead animals. The University of Georgia will be glad to identify any maggots of concern.

Current Situation

We have several factors working in our favor. (1) Fortunately the screwworm infestation is hundreds of miles south of Georgia, so the risk is small. However, we realize that thousands of vehicles move from Florida through Georgia every day, including many with pets or other animals. When these stop at service stations, restaurants, or welcome centers there is the risk that any hitch-hiking maggots could disembark and try to make a home in Georgia. (2) We’re moving into winter, so it will soon be too cold for screwworm flies to survive in Georgia. (3) And we have a very vigilant network of veterinarians who are attentively watching to ensure none of their patients have screwworms. We can anticipate that Florida will eradicate screwworms this fall and by the time spring begins to warm Georgia, there will be no risk of screwworms moving north to our state.

Additional Information

If you want to know more about screwworms (and how much we don’t want them back in the Southeast), talk with someone whose family had cattle back in the 1950s. They can tell you about digging maggots out of calves’ navels and smearing insecticides in dehorning and branding wounds. Florida has lots of good information about screwworms on their website at http://www.freshfromflorida.com/Divisions-Offices/Animal-Industry/Consumer-Resources/Reportable-Animal-Diseases/New-World-Screwworm.

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