By Stephanie Schupska
University of Georgia

Invasive fire ants plague most of the Southeast, rooting out native species and delivering blistering bites to whatever gets in their way. Amazingly they all likely came from fewer than a dozen stowaways that landed in Mobile, Ala., in the mid-1930s, says a University of Georgia researcher.

Using a bit of genetic sleuthing, Kenneth Ross, an entomologist with the UGA College of Agricultural Environmental Sciences, tracked the lineage of this notorious Southern pest. What he found surprised him.

“Most didn’t make it over on the boat,” Ross said. “When we look at the area around Mobile, the most probable number of queens is seven, eight, nine and at the minimum six.”

Ross worked to determine the number of queen ant colonizers with his former student DeWayne Shoemaker, who now works at the U.S. Department of Agriculture Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Fla.

They also used the genetic markers to pinpoint where the invasive fire ants, known scientifically as Solenopsis invicta, originated. Formosa, in northeast Argentina, looks to be the source population.

“In textbooks, they were saying Brazil,” he said, “but those ants look nothing genetically like the ones we have here.”

The Argentine queens set out on their journey accidentally, he said, either in soil or by landing on boats after their spring mating flight.

Fighting invasives

By tracing the U.S. fire ant population back to Argentina, scientists can determine how fast and how far other fire ant colonies can grow. Currently, Solenopsis invicta fire ants cover most of the central part of South America.

This information, Ross said, can help with the development of effective management practices based on the biology of an invasive species. It can help researchers predict other species’ invasive potential, too.

Since moving out of Alabama, the Argentine fire ants have spread like wildfire. Georgia got its first colonies in the 1950s. On their own, the ants have traveled as far north as North Carolina and as far west as Texas. With a little help, such as in nursery pots and soil, they have travelled as far as California.

Five years ago, they landed in China, stowing away from the U.S. “The fire ants are hopscotching along,” he said. The Solenopsis invicta is also found in Australia and the Philippines.

Despite prevention efforts, Ross predicts the fire ants will spread to even more tropical and semitropical countries in the next decades.

Stacks of research

Owing to the fire ant’s status as a major pest throughout much of the South, an enormous amount of research has been conducted on the basic biology of the species over the past 40 years, Ross said.

Fire ants have had a large negative impact on ground-nesting birds and insects. They’ve also driven out native species of fire ants, such as Georgia’s Solenopsis xylomi.

On the positive side, fire ants feed on agricultural pests in cotton, and their presence is associated with a decrease in the tick population. They also eat dead animals and any insects they can catch.

Fire ants tend aphids, which produce a substance the ants feed on called honeydew. Because the ants favor aphids and protect them from natural predators, ants are known as indirect pests, specifically in pecan production.