The aggressive ants also swarm over people, stinging multiple times with venom that induces a painful, fiery sensation. A white, fluid-filled pustule or blister develops a few days after the sting.
Some 500,000 people in the Southeast U.S. are at even greater risk because they are highly sensitive or allergic to the ant's venom, Porter said.
Fire ants feed on almost any plant or animal material, including vulnerable reptile and ground-bird hatchlings.
Fire ants are tied with snakes as the number one predator of eggs of the black-capped vireo, a ground-nesting bird, Vander Meer said.
A large population of the endangered bird is located at the U.S. Army's Fort Hood military installation in Texas.
"We have been working with military personnel there to develop repellents that will keep the ants away from the nests, and so far that looks like it's been very effective," he said.
USDA scientists are working on improving current bait systems and developing novel population suppression methods as alternatives to costly and environmentally damaging pesticides.
Porter first discovered phorid flies in 1989 while doing research in South America, where fire ant population levels are about five to ten times less than in the United States because of natural enemies.
In all, about 20 different species of phorid flies are known to attack the ants. A single species is unlikely to produce the desired impact on fire ant populations, Porter said, so a variety of the barely visible insects will be introduced.
Since 1997 three fly varieties have been released in almost all Southeastern states. Porter plans to introduce a fourth within the next month.
The flies are not a danger to animals or people.
"They're about as safe a biocontrol agent as you can get," Porter said. He hopes to start seeing a reduction in fire ant populations within five years.
"If we can bring natural enemies from South America here, we can reduce the ant population by 80 percent," Vander Meer said. "And that would be without using any chemical control at all."
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