Asian needle ants push into the Carolinas

CorrespondentMarch 17, 2013 

North Carolina has a new ant in town, and it’s tougher than we thought. In the national science journal PLoS One released this month, Jules Silverman, professor of entomology at N.C. State, and his Ph.D. student show that the stinging Asian needle ant is tearing across our state’s landscape. Pushing out another well-established ant species, the Asian needle ant commands attention.

I have a close-up perspective on this: I was Silverman’s Ph.D. student, and this was my research. I’ve since moved out of academia and into science journalism. But touching base with those still involved in this research made me feel like, well, a zoological battlefield correspondent.

This is an intra-species war.

Early reports

Our discovery of the Asian needle ant’s aggressive trek started five years ago at an office park in Morrisville, just northwest of Cary. While helping fellow researchers with their work on Argentine ants – another invasive pest that has staked its claim across the Carolinas – we noticed something strange creeping through Argentine ant nests.

About the length of a pencil eraser, these skinny and shiny black ants crawled close to the ground.

“At first, we couldn’t quite figure out who they were,” said Alexei Rowles, then a postdoctoral fellow in Silverman’s lab. “But then we heard of some other research of a newly invasive pest in forests: the Asian needle ant. At the time, it didn’t even have a common name.”

Silverman was struck by the Asian needle ant’s persistence in Argentine ant territory. “It’s highly unusual to find other ant species sharing space with Argentine ants,” he said recently.

Why so unusual?

While most ant species fight between nests, the small, reddish-brown Argentine ants have inter-nest harmony, with workers flowing peacefully in and out of one another’s nests. This results in huge colonies, called “supercolonies,” with millions of workers and thousands of queens.

“One supercolony spans the entire Mediterranean coastline. That’s more than a thousand miles of ants,” Rowles said.

Although they get along well with one another, Argentine ants are extremely aggressive toward other ant species.

They use their tremendous populations to consume as much food and livable space as they can. Feisty fighters, Argentine ants don’t have stingers. Instead, they aggressively outnumber their competition.

“Argentine ants are invasive on every continent except Antarctica, and they devastate the native fauna where they invade,” Rowles said. “Also, they invade people’s homes.”

Silverman agrees.

“Of all the invasive species on Earth, the Argentine ant is ranked one of the world’s worst 100 for the cascading negative impacts they have on environments they invade. They just don’t tolerate many other species.”

A new bully in town

Because the Argentine ant has such well-established territories, we took notice that day in Morrisville when we first saw the Asian needle ants making their appearance in Argentine ant territory.

Over the next four years, we monitored Asian needle and Argentine ant nests around trees and found that, not only were Asian needle ants sharing territory with Argentine ants, over time the Asian needle ants were pushing Argentine ants out of the system.

“It’s extremely rare to find other ant species sharing nest space with Argentine ants. But more surprising is that another species would actually displace the Argentine ant,” Silverman said.

While not aggressive like Argentine or fire ants, Asian needle ant stings can pack a punch. They nest anywhere from mulch piles to under rocks or doormats. And because their nests aren’t conspicuous mounds like those of fire ants, people might get stung without noticing they’re grabbing a nest filled with stingers.

Research shows people are more often allergic to Asian needle ant venom than to honeybee venom.

People who aren’t allergic to honeybees might be allergic to Asian needle ants because their venom is of a different chemical formula.

An early start

One secret to the Asian needle ants’ success? Their hardy nature.

“We show Asian needle ants are active two months earlier in the year than Argentine ants and survive colder temperatures longer,” Silverman said.

This means that Asian needle ants are setting up their houses while Argentine ants are still deep in winter’s sleep. By the time Argentine ants emerge, Asian needle ants already have established their nests.

The Asian needle ant’s headway is no surprise to Holly Menninger, director of public science for NCSU’s Your Wild Life program, whose School of Ants project finds this new invader everywhere it looks. With School of Ants, citizens mail ants from backyards across the United States to NCSU, and researchers identify them. The project is finding new records of Asian needle ants as far north as New York and as far west as Washington state.

“Five years ago, nobody knew what the Asian needle ant was,” Menninger said. “Today, it’s one of the most common ants found in the United States.”

For now, Silverman’s lab focuses on Asian needle ant behavior and how to keep this invader out of our homes.

Eleanor Spicer Rice is senior science editor at www.verdantword.com. She is the author of “Dr. Eleanor’s Book of Common Ants,” to be published in April. Details: www.yourwildlife.org/dr-eleanor-spicer-rice.

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