What would fire ants mean in our region?

As we’ve learned from the Chestnut blight and the hemlock woolly adelgid, invasive species can have a huge impact on our forests. So when an observant gardener recently told us that fire ants seem to be moving out of the Piedmont and into the mountains, we were all ears. Although no Coweeta LTER researchers are currently studying fire ants, we decided to look into this invasion in more detail.

The most common invasive fire ant is the Solenopsis invicta, more commonly known as the red imported fire ant. According to the USDA, the red imported fire ant probably entered the US in the late 1930s when it was brought to Mobile, Alabama in soil used as ballast for cargo ships. The ant has since spread across much of the southeast and California, including neighboring areas of South Carolina, Tennessee, Georgia, and in Cherokee and Clay Counties in North Carolina. It’s unlikely that invasive fire ants will wipe out all of our native ants because they typically avoid forests in favor of disturbed lands such as pastures, recreational facilities, lawns, and roadsides.

Imported fire ants cause significant damage by harming human health, feeding on a wide range of crops and helpful soil organisms, killing farm animals and wildlife, and even damaging infrastructure. The estimated cost of control, medical treatment, and damage to property in the U.S. is estimated at $6 billion annually. Although these ants have more than 30 species of natural enemies in South America, they are susceptible to only a few predators, parasites, and diseases in North America.

Coweeta LTER research has shown that little ants make a big difference. They are predators, prey, scavengers, and the most important dispersers of seeds in Eastern deciduous forests. By secreting anti-microbial chemicals and competing with termites and fungi for nests, they also slow the decomposition of large wood in the forests. Through all of these activities, ants play a surprisingly important role in shaping microhabitats, nutrient flows, and plant distribution in our forests.

Just consider the spring wildflowers. They and our native ants have a mutually beneficial relationship (called a mutualism) through which plants produce fruit to feed the ants and ants spread the seeds contained within the fruit to assist in the plants’ reproduction. Coweeta LTER researcher Robert Warren and his colleagues have shown that these mutualisms depend on changes in temperature, light and moisture in the spring. However, there is evidence that climate change is disrupting these mutualisms.

Not all plants and ants are adapting to climate change at the same rate, so some of the earliest spring ephemerals (short-lived) are emerging earlier in the year only to find that the ants who usually spread their seeds are still in the ground. Over the years, this could lead to a shrinking population of early-flowering plants, a growing population of later-flowering plants, and possibly a cascade of other effects. Warren’s research also shows that increasing temperatures are also leading some ant species to migrate uphill, further changing ant-ant interactions and ant-plant interactions.

Those same increasing temperatures might explain why the fire ant is moving into the mountains. Paradoxically, more intensified droughts that go hand in hand with changing climate might actually have an unforeseen benefit and prove unfavorable. On the other hand, it is possible that some of the climate changes we will experience— such as more intensified droughts—may prove unfavorable to this moisture-loving species of fire ant.

Historically, management of red imported fire ants has depended on chemical insecticides, but University of Georgia alumnus Reid Ipser and other researchers are examining non-polluting biological controls as well. For example, Ipser’s research showed that native species can compete effectively against fire ants and thus supporting native ant populations might be an important alternative or complement to insecticide use. Another researcher collaborating with Coweeta LTER scientists, Josh King, at the University of Central Florida, has shown that “disturbance” (e.g. clearing trees, doing building work, etc.) is what facilitates the movement of fire ants. Based on his research, perhaps if we take care to minimize “disturbance” as we road build, etc., we might limit fire ants, as might trying to recover those disturbed areas with tree cover.


This column is produced by members of the Coweeta Listening Project (CLP), a branch of the Coweeta Long Term Ecological Research Program. Views expressed here are not representative of the USDA Forest Service or the Coweeta Hydrologic Lab. Please share questions, comments, or suggestions for future topics at cwtlistn@uga.edu or Coweeta Listening Project, UGA, 210 Field St., Room 204, Athens, Georgia 30602.


Original Citation: The Coweeta Listening Project. Franklin Press. Column on "Science, Public Policy, Community." Page B4. May 24, 2013.