 most often occur at mid-morning 1 or 2 days following a rainfall if the temperature is above 22°C and the wind is light. At this time a virgin female flies into a cloud of congregating males and mates in the air. The male subsequently dies while the female seeks a location to start a new colony. Once located, she breaks off her wings and excavates a brood chamber approximately 1 to 2 inches below ground. The new queen subsequently deposits a few dozen eggs which hatch in a little over a week. The queen does not forage but feeds the first generation of larvae from nutrients obtained from her fat reserves and by dissolving her no longer needed wing muscles. The larvae obtain the nutrients by trophollaxisis (exchange of alimentary fluids) or from sterile eggs she has produced for that purpose. The entire life cycle is completed in 3 to 4 weeks.
The initial generation of adult worker (minims) are relatively small due to a limited amount of nutrients available from the queen. Once developed these worker open up the brood chamber and begin to forage for available food. Soon another generation of larger adult workers has developed and the colony begins to grow. Workers start to emerge daily and within 6 months the colony population approaches several thousand and an above ground mound is visible. The polymorphic (poly in Latin means many and morph means form) nature of the worker becomes more apparent. The largest workers in the colony (majors) can be as much as 10 times the size of the smallest workers (media). The queen lives up to 7 years and produces an average of 1600 eggs per day. At maturity, a monogynous (one queen) fire ant colony can consist of over 250,000 ants. As discussed above some fire ant colonies have only one queen per nest while others can have many queens and are called polygynous colonies. The polygynous colony may be more difficult to control because all the queens must be killed to prevent the colony from surviving. Polygynous colonies frequently expand by "budding"; i.e., some of the queens and 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