Parasitic Flies Turn Fire Ants Into Zombies

By Bill Hanna, Fort Worth Star-Telegram Bill Hanna, Fort Worth Star

It sounds like something out of science fiction: zombie fire ants. But it's all too real. Fire ants wander aimlessly away from the mound. Eventually their heads fall off, and they die.

The strange part is that researchers at the University of Texas at Austin and Texas A&M's AgriLife Extension Service say making "zombies" out of fire ants is a good thing.

"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 the 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 there are as many as 23 phorid species along with pathogens that attack fire ants to keep their population and movements under control. So far, four phorid species have been introduced in Texas .

The flies "dive-bomb" the fire ants and lay eggs. The maggot that hatches inside the ant eats away at the brain, and the ant starts exhibiting what some might say is zombie-like behavior. "At some point, the ant gets up and starts wandering," said Rob Plowes, a research associate at UT.

The maggot eventually migrates into the ant's head, but 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. This wandering stage goes on for about two weeks".About a month after the egg is laid, the ant's head falls off 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. "Just one or two flies can control movement or above-ground activity," Plowes said. "It's kind of like a medieval activity where you're putting a castle under siege."

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 south of the Metroplex at farms and ranches from Stephenville to Overton . It is the fourth species introduced in Texas .

Fire ants cost the Texas 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.

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."

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.