WASHINGTON -- The ferocious fire ant, builder of mounds across the South and source of a painful bite that can kill allergic people and livestock, is about to get reacquainted with an old enemy.
Department of Agriculture scientists in Gainesville, Fla., this week will begin releasing several thousand Brazilian phorid flies in the first attempt to use nature against the accidentally imported fire ant.
"This is the first real shot we've got at biological control," said Sanford Porter, an entomologist with the agency's Agricultural Research Service. "It will not eradicate them, but if it would drive down the populations, everybody would be thrilled."
If the tests in Florida are successful, in a few years the pinhead-sized flies could be used to control fire ants on the 278 million acres in 11 states and Puerto Rico that are now infested, Mr. Porter said.
"If the results look positive, we'd like to release them in dozens or hundreds of sites around the United States and let them spread naturally," he said.
The reddish-brown fire ant first came to the United States about 60 years ago, probably stowed away aboard a ship from South America. The ants are native to the drainage basin of the Paraguay River.
Since then, the ants have flourished from Florida to Texas and as far north as Tennessee and southern Virginia, where they enjoy warm temperatures and have no natural enemies. Anyone who has gazed at a Southern pasture has seen fire ant mounds, and many a golfer, picnicker or barefoot stroller has suffered a blistering bite.
Besides the nuisance factor, Mr. Porter said up to 2 percent of the people in America are allergic to fire ant venom. When bitten, they can go into shock or in severe cases even die.
The aggressive ants also have been known to kill weakened calves or other livestock and cause infections in healthy animals. They have ruined soybean fields by sucking the sap out of plants, chewed up potatoes and strawberries and even undermined rural roads by building intricate tunnels that cause potholes.
"They get into virtually everything possible," Mr. Porter said.
Pesticides have proved successful against the fire ant, but they must be used repeatedly and are not practical or cost-effective over large tracts of land. In addition, some pesticides kill other native ants and beneficial small animals such as lizards and mice.
Enter the phorid fly.
The mortal enemy of the fire ant in South America doesn't actually attack the ant, but its work is no less gruesome or effective. Instead, it lays a torpedo-shaped egg inside the ant's body.
After a couple of weeks, the egg develops into a larvae that works its way into the ant's head and eventually causes the head to simply fall off. Then the larvae uses the shelter of the head to grow into an adult fly.
Fire ants tested by scientists are deathly afraid of the phorid fly.
"Whenever the flies show up, the ants freeze. They refuse to move, they stop foraging," Mr. Porter said.
After three years of laboratory testing, scientists believe the phorid fly will target only the fire ant and will not become a new pest causing unforeseen problems in North America. The flies also are not attracted to human food or waste and pose no threat to people.
In South America, the fire ant population per square yard is about one-fifth of that in the United States, largely because of natural enemies such as the phorid fly, Mr. Porter said.
Two other biological controls are being examined: a microbe that causes disease in worker ants and a parasitic ant that debilitates the fire ant queen and causes her to lay fewer eggs.
"The combined effects would tilt the balance in favor of our native ants," Mr. Porter said. "The fire ants would no longer be the dominant ant that controls everything out there."