Although the Asian needle ants did kill more Argentine ants once they had claimed territory, the researchers wondered how the less numerous insects were gaining a leg—or six—up. Cold-tolerance tests in the lab hinted that Asian needle ants were better adapted to the temperate North Carolina climate than the tropical Argentine ants. The Asian needle ants shook off their winter sluggishness as early as March whereas the Argentine ants did not resume activities until late April or early May, the researchers reported on February 8 in PLoS ONE.
An Asian needle ant takeover would not only be bad news for Argentines but also native ants—and for humans as well. Their burning stings can induce a life-threatening allergic reaction in sensitive individuals. “More people are allergic to Asian ant stings than to honeybee stings,” Spicer Rice says.
The fierceness of the Argentines wouldn’t allow them to be pegged as pushovers and suggests that understanding how invasive species react to new climate is important to predict their spread. The Asian needle ant may be winning the war in North Carolina simply because the state is at the northern limit of the Argentine ants’ range, Spicer Rice says—or it could be poised to become the next threatening invasive species.
Another project led by N.C. State researchers could reveal if Asian needle ants are the next big ant threat. The project, School of Ants, asks citizen scientists to help catalogue the species in urban areas by sending in the insects they find. The researchers are particularly interested in the spread of the Asian needle ant and have discovered specimens from locations as widely separated as New York City and Washington State.
The first record of Asian needle ants in the U.S. dates from the 1930s in Louisiana, indicating the insect was probably a ship stowaway. Like the Argentine ant, the Asian needlers form colonies with thousands of workers and many queens, Pedersen says. Unlike other species that fly to new locations, invasive ants are able to mate within a single colony. As a result, a single cup of soil, perhaps stored with vegetables or flowers, can hold enough individuals to gain a foothold on a new continent.
Climate change, human movements and disrupted habitats offer new opportunities for invading ants, Pedersen says. “In general we will see more ant species being invasive, and here we already have a new member of the crew—the Asian needle ant,” he says.