“In the last five years, the range of RIFA has continued to spread north and west as mild winters have allowed them to become established and they have adapted to colder temperatures,” Tredway says.
Fire ants move from location to location by both artificial and natural means. Naturally, newly mated fire ant queens fly into new areas, often assisted by wind currents, says Dr. Kelly Loftin, an extension entomologist at the University of Arkansas.
In addition, during floods entire fire ant colonies will form rafts in floodwater and move with the floodwater until they reach dry ground, then exit and build a new colony, he says. Artificially, fire ant colonies or newly mated queens harbor in infested grass sod, beehives, nursery stock or baled hay stored in contact with the soil. When these infested products are moved to new areas, colonies are likely to form and golf courses not infested with fire ants soon become inundated.
The current U.S. distribution of red imported fire ants is generally stable and includes a contiguous range from western Texas across the Southeast and up the eastern seaboard states into Virginia, says Dr. Robert Puckett, assistant professor and extension entomologist at Texas A&M University. Additionally, fire ants occur in New Mexico, Arizona, Nevada, and California. They are also found in Oklahoma, Arkansas, Missouri and Tennessee. “Expansion along the boundaries of the known range has slowed over the past decade or two because these ants now occupy the majority of area of the United States that has suitable habitat and climate for them,” Puckett says.
USDA ARS modeling suggests that imported fire ants could move 50 to 100 miles northward in Oklahoma and continue expanding their range into parts of Virginia, Maryland and possibly Delaware, according to Loftin. “In the western U.S., they may expand into certain portions of New Mexico, Arizona, California, Oregon and Nevada,” he says.
Dr. Timothy Davis, University of Georgia Chatham County extension coordinator/Chatham County ANR extension agent, says fire ants will probably be limited by two factors: moisture and temperature. “We have seen some locations that would normally be too dry, but fire ants have survived due to irrigation practices supplying sufficient moisture for their populations,” he adds. “We have also seen their range expand over several mild winters only to be pushed back with a colder winter in some locations along the northern edge of their range. Of course, the current warming trends in climate change are to the advantage of fire ants and many other invasive species.”
Fire ants continue to move slowly north and west. States on the northern edges of the fire ant quarantine, such as Kentucky, North Carolina, West Virginia and Virginia, are beginning to see their first fire ant problems. “On the northern edges, fire ant range expansion is generally limited by cold,” he says. “However, climate change and, in some regions, hybridization with more cold-tolerant black fire ants, may help the ants move into new territory. In the west, moisture is generally the limiting factor. In these areas, ants are still able to move into golf courses and other urban sites with artificial irrigation.”
John Torsiello is a Torrington-Conn.-based writer and frequent GCI contributor.