FORT WORTH, Texas -- Some researchers in Texas are trying an unusual approach to combat fire ants -- parasitic flies that turn the pesky insects into zombies whose heads fall off.

"It's a tool. They're not going to completely wipe out the fire ant, but it's a way to control their population," said Scott Ludwig, an integrated pest management specialist with Texas A&M's AgriLife Extension Service in Overton, in East Texas.

The tool is the tiny phorid fly, native to a region of South America where the fire ants in Texas originated. Researchers have learned that as many as 23 phorid species along with pathogens attack fire ants to keep their population and movements under control.

So far, four phorid species have been introduced in Texas, where fire ants cost the economy about $1 billion annually by damaging circuit breakers and other electrical equipment, according to a Texas A&M study. They can also threaten young calves.

The flies "dive-bomb" the fire ants and lay eggs, and then the maggot that hatches inside the ant eats away at the brain. Later, the ant gets up and starts wandering for about two weeks, said Rob Plowes, a research associate at the University of Texas at Austin.

Although the ant exhibits zombie-like behavior, Plowes said he "wouldn't use the word 'control' to describe what is happening. There is no brain left in the ant, and the ant just starts wandering aimlessly."

About a month after the egg is laid, the ant's head falls off and it dies -- and the fly emerges ready to attack any foraging ants away from the mound and lay eggs.

Plowes said fire ants are "very aware" of these tiny flies, and it only takes a few to cause the ants to modify their behavior.

"It's kind of like a medieval activity where you're putting a castle under siege," Plowes told the Fort Worth Star-Telegram for a story in Tuesday editions.

Researchers began introducing phorid species in Texas in 1999. The first species has traveled all the way from Central and South Texas to the Oklahoma border. This year, UT researchers will add colonies at farms and ranches from Stephenville to Overton. It is the fourth species introduced in Texas.

The flies, which are USDA approved, do not attack native ants or species and have been introduced in other Gulf Coast states, Plowes said. Despite initial concerns, farmers and ranchers have been willing to let researchers use their property to establish colonies. At the Texas and Southwestern Cattle Raisers Association in Fort Worth in March, Plowes said they found plenty of volunteers.

Determining whether the phorid flies will work in Texas will take time, perhaps as long as a decade.

"These are very slow-acting," Plowes said. "It's more like a cumulative impact measured across a time frame of years. It's not an immediate silver-bullet impact."