The red imported fire ant (solenopsis invicta) was introduced in the United States around the 1930s. They marched across the entire south and now take up residence in 15 states. They have caused death and they aren’t preventable. So how does one control them? To find out, Lawn & Landscape spoke with Bastiaan “Bart” Drees, professor of entomology and extension specialist at Texas A&M University.
“The real key feature is there is no central opening from which ants enter and leave the colony in the top of the center of the mound,” Drees says. “Many of our native ants will not have that kind of characteristic.”
Another feature that makes identifying fire ants easy is the behavioral reaction of the worker ants. The colony that creates the mound is known to have up to 200,000 worker ants and one or two queen ants.
“The worker ants will scale and run up very quickly in mass on vertical surfaces,” Drees says. “If you see an ant hill or a suspected ant hill, and you put a stick in it – and if the temperature is above 55 or 65 degrees – in seconds that stick will be completely covered in ants.”
Native ants run around the stick. If you stick your foot in a red imported fire ant mound, the ants will run up your leg biting and stinging, and their venom will create a burning, on-fire sensation – hence their name. About 1 percent of the U.S. population is hypersensitive to insect venom, including fire ants, and can actually die from the attack.
Fire ants can build mounds everywhere. And they don’t have a dormant season, though they’re more active in spring and fall.
“They prefer open sunny areas,” Drees says. “They are often nesting right in the middle of turfgrass areas.”
The ants can nest in shaded areas and are known to invade houses, hiding in walls and closets.
In addition, colonies that contain multiple queens spread through migration. Throughout the year, they’ll move above and below the surface and can move 75 feet or more almost overnight.
“That is what really bothers people in the South because they’ll spend all the time and effort and money to get rid of the ants,” Drees says. “The ant nests from the neighboring properties can hike into their beautiful ant-free zone overnight and reestablish a colony on that property.”
Still, there are methods for control. Drees recommends a two-step method.
“There are other approaches, and the two-step method is not appropriate in all situations,” he says. “But for large landscape areas where fire ant suppression, not eradication, but about 90 percent in reduction is acceptable, the two-step-method is probably the most cost effective and environmentally friendly approach.”
The program starts with using fire ant bait.
“These are insecticides that are dissolved in soybean oil and about 1 percent or less of the soybean oil contains that active ingredient,” Drees says. “You use some kind of broadcast seeder or handheld seeder or special equipment to spread this evenly across the entire lawn. The application rate is usually about 1- to 1 ½- pounds per acre, which is a very small amount.”
Depending on the active ingredient, a broadcast application can eliminate 80 to 90 percent of the mounds and the colonies nesting below ground, Drees says. For the remaining nuisance mounds, a mound treatment can be bought from hardware and big-box stores.
“The result is that you use the least amount of pesticide possible to reduce these ants,” Drees says.
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