Forty Acres Field Guide: Red Imported Fire Ant

By Dorothy Guerrero in 40 Acres Field Guide, July | August 2013 on June 25, 2013 at 12:15 pm | No Comments

UT is an urban university in the heart of the city, yet the campus and its environs teem with fascinating plants and animals—from tropical parakeets to the world’s weirdest cactus.

Red Imported Fire Ant
(Solenopsis invicta)

What’s worse than a sugary-looking mound of crawling, bulbous, blood-red fire ants? Zombie fire ants.

The natural predator of the imported fire ant is the female phorid fly, a tiny insect that chases the ants as theymarch along a trail in search of food. The fly lands on her target and quickly injects one of her eggs near the ant’s thorax. The ant reacts like it has been shot—becoming partially paralyzed and confused before limping back to the mound. After developing, the larva cruises around the ant’s body, feeding on its blood and growing larger, eventually making its home inside the ant’s head and devouring its jaw muscles for fuel. At this point, the ant’s brain is still functioning, but the larva can control the body and walk it to a safe nesting place. Hence the term “zombie ants.” The head eventually falls off and roughly 45 days later, an adult fly emerges from the poor ant’s decapitated shell.

Larry Gilbert, BA ’66, has devoted more than 30 years to studying this grisly scenario as director of UT’s Brackenridge Field Laboratory on Lake Austin Boulevard. He and his colleagues have been researching the effects of introducing the phorid fly into the U.S. to combat the dreaded fire ant.

Imported fire ants—not to be confused with native fire ants—most likely made their way to our front yards as stowaways on ships from Brazil and Argentina in the 1930s. Because they had no natural predators here, the ants thrived and spread west to Texas and beyond. While most people are searching for a way to eradicate the species or “nuke ’em,” as Gilbert says, he and his team believe in playing the long game. Their research suggests that deploying their natural enemy, the phorid fly, is a safer and more economical way to control them than pesticides. In South America, where fire ants and phorid flies coexist, fire ants aren’t considered persistent pests.

When he was a fourth-grader in Jones Creek, Texas, Gilbert remembers taking one wrong step with his broken foot into a pile of fire ants. They swarmed his cast and buried themselves deep between his toes. The pain and burning, he says, was unbearable. When asked why he has devoted so much of his life to the study of fire ants, Gilbert’s eyes brighten and a weathered smile spreads across his face. “Self-defense,” he says.

To read the rest of the Forty Acres Field Guide, click here.

Illustration by Jason Holley.

Tags: Brackenridge Field Laboratory, Larry Gilbert, phorid fly, zombie ants