A new (old), invasive ant in the hardwood forests of Eastern North America and its potentially widespread impacts

BENOIT GUENARD1,2, ROBERT R. DUNN1,2 PLoS ONE (2010)  [ Full article ] 1 - Department of Biology, NC State University, Raleigh NC, 27695, USA 2 - W. M. Keck Center for Behavioral Biology, NCSU, Raleigh NC, USA * E-mail contact: bsguenar@ncsu.edu

This week, scientists from North Carolina State University have documented the spread and consequences of a new invasive ant, the Asian Needle Ant (Pachycondyla chinensis). A number of invasive ant species have now spread across eastern North America, including fire ants (Solenopsis invicta) and Argentine ants (Linepithema humile). Like these species, the Asian Needle Ant is expanding its range and, where present, meting out consequences, both for humans (through its painful stings) and for native wildlife. Unlike these species, the Asian Needle Ant appears to reach its greatest abundances in forests.

Eastern North America is home to hundreds of species of native ants, species that carry out necessary ecological processes and, for the most part, remain relatively poorly studied. We know little enough about these species, that it is easy for a new species here and there to go missed. Such was the case for the Asian Needle Ant, which arrived in the U.S. from Japan no later than the 1930s but went for the most part unremarked upon for more than seventy years. It was known to be present, but regarded as rare and innocuous. Then, at some unrecorded point, things began to change.  In the last few years, more and more sightings of this species have been confirmed. Equally worrisome, the sting of this species was recently shown to cause anaphylaxis in a high proportion of individuals who are stung. The rate of anaphylaxis in the Asian Needle Ant is fourfold that due to honeybee stings. Still, the species, for the most part, continued to go largely unstudied. One thesis project was conducted on it at Clemson University, but went unpublished. One study in Manhattan found it to be present but inconsequential on Broadway, not far from where the show must go on. But little else was done or noted about the species, until 2006.

In 2006, when Benoit Guénard moved from Montreal to Raleigh, with eyes to find and know all of the ant species of North Carolina, he quickly discovered that Asian Needle ant was not only present in the area, but, in fact, present in nearly every forest in which he turned logs and hiked around. What was more, where it was present the native wildlife seemed to be, at least in part, missing! It was at this point that Guénard decided to study how the ants present in areas invaded by the Asian Needle Ant compare to those present in matched sites where the Asian Needle Ant was absent. Guénard, along with his advisor Rob Dunn, report on this work in a new article in the journal PLoS1. Guénard found what his initial observations suggested, that Asian Needle Ant is, in many areas, very abundant (in essence, twice as abundant as all of the other ant species combined) and where it is abundant many native species are rarer than they would be otherwise. There were complexities, too. Some native ant species appear to do better where the Asian Needle Ant is present. Just why, he does not yet know.

The disruption of native ants and other groups of insects, such as termites, could have important impacts on ecosystems services provided by these organisms. For instance, several species of ants of the genus Aphaenogaster tended to be very rare where the Asian Needle Ant was common. These native ants are well known for their important role of seed dispersers of many understory plants such as Ginger, Trillium, Violet and Bloodroot. Their loss from local forests could lead to the local extinction of some ant-dispersed plants, particularly those that are unable to reproduce vegetatively. Similarly, the reduction of termite populations within forests could decrease the decomposition rate of wood, with knock on effects on the recycling of nutrients and even the growth of trees. Such effects are still speculative, but possible. They may be occurring, undocumented, in your backyard right now.