Fire ant mounds are the aboveground part of the fire ant nest. It is the only part of the fire ant nest that is visible. Scientists think that they fire ants make the mounds as a way to get the queen out of the damp ground in rainy weather.
Fire ants also make mounds in winter. They move the queen and the immature ants up into the mound during the day. The mound absorbs the sunshine, so it is warm inside. At night, the workers move the queen back down into the tunnels underground.
In areas where fire ants are common, there can be hundreds of colonies per acre. Many homeowners do not see the foraging fire ant workers, so they do not think that fire ants have invaded their yard. When the ants finally make a mound, the surprised homeowners think the ants have just arrived.
As the fire ant colony grows, the workers make the mound larger. A mound can easily reach 18″ high and 24″ in diameter. Depending on the type of soil, many fire ant mounds can repel rain. Mounds that have been standing for a long time have been known to damage farm equipment.
Fire ant mounds can damage lawns. The damage to the grass can be a nuisance in a home lawn, but it can be expensive in a golf course. Fire ant mounds can be unsightly in athletic fields and the ants can be a threat o the players who use the field.
In addition to making mounds in the lawn, fire ants also make dirt mounds when they nest in bath traps under homes. Homeowners discover soil coming out from under a baseboard. They are usually disturbed to discover fire ants behind the tub.
Fire ants also bring soil into electrical equipment and other places where they nest. Maintenance workers often find fire ants inside of traffic light switch boxes and airport runway lights.