Fire ants adapted to march through northern Georgia

ALBANY, Ga. -- For years, experts predicted fire ants couldn't tolerate frosty winters in the north Georgia mountains. But the aggressive, fast-breeding South American pests have defied predictions, spelling trouble for crops, wildlife and people.

Fire ants have spread to all of Georgia's 159 counties and a new type discovered in the Rome area seems especially adept at hunkering deep in the ground to escape the cold, said Wayne Gardner, a University of Georgia entomologist.

With no natural enemies outside South America, fire ants have spread across about 275 million acres in the past 80 years, mostly in southeastern United States. Isolated colonies have also been found in Delaware, New Mexico and California. They've also turned up in Australia.

The aggressive predators, which crowd out native ants, live in the ground and build mounds above their colonies.

Fire ants feed on crop seedlings and can damage farm machinery by their mounds. When disturbed, they swarm out of their nests and sting repeatedly, and can kill newborn deer and quail hatchlings.

Their stings usually cause only pain and discomfort to humans, but can prove fatal to people allergic to their venom.

There are two main types of imported fire ants: red and black.

The black type is believed to have arrived about 1918 in Mobile, Ala., in dirt that was used as ship's ballast. The red is believed to have arrived in Mobile the same way in the 1920s. The black spread to Mississippi and Alabama, while the red spread beyond to other states.

Before the discovery of fire ants in northwest Georgia's Floyd County, scientists had assumed they would not be able to survive in the northern third of the state, Gardner said.

But a Floyd County extension agent discovered fire ants in 1985. Then a U.S. Department of Agriculture Laboratory determined they were hybrids -- a cross between reds and blacks.

By 1998, the ants had been seen in every county.

"Basically we were hit from two sides," Gardner said. "It (the red fire ant) came from the southwest and moved across the state, but we also had this hybrid that moved in from Alabama into the northeastern part of the state. So it covered the state a lot quicker."

The hybrids and the reds look identical, Gardner said. It takes a laboratory test to tell them apart.

"The hybrid forms may have adapted some sort of behavior that allows them to survive when the temperature drops," Gardner said. "Or they may travel farther underground than the red ants. We just don't know yet."

There is no reliable way to eradicate fire ants, even though Americans spend millions of dollars a year on chemicals for temporary control. One fire ant colony can contain between 100,000 and 300,000 worker ants and each colony produces several hundred queens every summer.