 workers break off from the parent colony and start a new mound nearby. This process in polygynous colonies can accounts for much higher mound density which sometimes approaching 1,000 mounds per acre.
Different sized worker adults. Image courtesy of USDA Archives.
One of the identifying characteristics of an imported red fire ant colony is the earthen nest or mound. This mound is a cone-shaped dome with a hard crust. They averages 1 ½ feet in diameter and 8-inches in height. In heavy clay soils they can exceed 3-feet in height and 4 1/2 feet diameter. There are usually no external openings in the mound; but tunnels a few inches below the surface tunnels radiate several feet from the mound allowing foraging workers access to the colony. These mounds serves several functions: They act as a flight platform for nuptial flights and to raise the colony above ground in excessively wet soil while protecting it above ground from intruders and rain. They also serve as a passive solar collector to supply warmth to the colony during the cold winter months.
Mound of red imported fire ant. Image courtesy of USDA Archives.
In areas with hot, dry summers these mounds may not be maintained or may not be formed at all. In a dark, protected site with sufficient moisture and an adequate supply of food, fire ants will nest in a wide variety of locations (e.g. rotten logs, walls of buildings, under sidewalks and roads, in automobiles, in dried cow manure).
Fire ants are omnivorous, feeding on almost any plant or animal material; although dead and living insects seem to be their preferred food. In rural habitats, they have a major impact on ground nesting animals (birds, reptiles, mammals). Studies have shown that once established in a new area there is typically a minimum of a two-fold reduction in the populations of field mice, snakes, turtles and other vertebrates and a maximum of a total elimination of some species. Fire ants also feed on plants attacking young saplings and seedlings, destroying buds and developing fruits and have been shown to feed on the seeds of over a hundred species of native wildflowers and grasses.
Damage to plants is increased during periods of drought as fire ants
seek alternate water sources. In fields where drip irrigation is used, these
insects build their mounds over the emitters reducing or blocking the flow of
water to crops. In some cases, actual physical destruction of microsprinkler
assemblies has occurred. Finally, the mere presence of fire ants on plants and
within the field will deter hand-harvesting of crops.
As an urban pest, imported fire ants cause many of the same problems experienced in rural areas. In addition they nest within the walls of homes and offices. Colonies are established under sidewalks and roadways frequently resulting in complete collapse of sections of these structures if the nests are eventually abandoned. The presence of fire ants can deter outdoor activities in yards, parks and school grounds. Home invasions can threaten small children and the elderly. House invasions are especially prevalent during periods of heavy precipitation and flooding. Fire ant colonies have been found inside automobiles, trucks and recreation vehicles resulting in traffic accidents caused by fire ants stinging the drivers. Imported fire ants are attracted by electrical currents and have caused considerable damage to heat pumps, air conditioners, telephone junction boxes, transformers, traffic lights, and gasoline pumps.
Because of their reputation people fear fire ants. In some areas playgrounds, parks, and picnic areas are rarely used because of the presence of fire ants. In campsites of state and national parks in fire ant infested areas, it is often difficult to put up or take down a tent without being stung by angry ants.
Stings. Fire ants are best known for their behavior of stinging, frequently in mass. If a nest is disturbed hundreds if not thousands of ants will quickly emerge and attack the intruder. This occurs so quickly and in mass that is not uncommon to have hundreds on the victim before