Identification

What are Red Imported Fire Ants? What makes them different from the native Southern Fire Ant?
It is important to understand that identification of Red Imported Fire Ants by their appearance is best left to experienced biologists. Red Imported Fire Ants are between 1/16 to 1/4-inch in length, reddish-brown in color and extremely aggressive in behavior. They usually produce mounds of soft, crumbly soil that contain their colonies. When these colonies are disturbed by ground vibrations from footsteps, flooding from watering, or being uncovered and exposed to sunlight, the worker ants characteristically "boil out" of the mound and aggressively swarm over a victim and sting repeatedly. In appearance the native Southern Fire Ant closely resembles the Red Imported Fire Ant.

How can you tell the difference between Red Imported Fire Ants and native Southern Fire Ants?
It's not easy and best left to the experts, since many of the external differences between Red Imported Fire Ants and native Southern Fire Ants can only be seen when magnified. Red Imported Fire Ant workers can be the same size and general appearance as native Southern Fire Ant workers, but come in a variety of sizes with the largest workers 2 or 3 times larger than the smallest. In addition, native Southern Fire Ants are less common in areas already infested with Red Imported Fire Ants.

Single and multiple queen Red Imported Fire Ant mounds. (Photo/Texas A&M University)

What do Red Imported Fire Ant mounds look like?
There are several behavioral characteristics that identify this insect pest. One of the characteristics of the Red Imported Fire Ant is the type of mound it constructs.

Unlike native ants, Red Imported Fire Ant mounds do not have one central opening into the colony. An extensive tunneling system is present within the mound. Red Imported Fire Ant mounds in California are unique from fire ant mounds found in the Southeast. In the Southeast, mounds typically look like those of a busy gopher, with crumbly soil piled up to 18 inches high. In California, most Red Imported Fire Ant mounds look more like flat patches of soil. These low mounds primarily occur when the colony is immature, or because the mound has been knocked down due to mowing or other disturbances.

Red Imported Fire Ants build their mounds in almost any type of soil, in open, sunny areas including pastures, parks, lawns, meadows and cultivated fields. Mounds can also be located in rotting logs, and around stumps and the base of trees. Colonies have been found in building wall cavities, or below foundations.

Colonies frequently migrate from one site to another in search of food and better conditions. The queen needs only about six workers to start a new colony. Almost overnight, they can develop a new mound several hundred feet away from their previous location.

What is the difference between single queen and multiple queen colonies of the Red Imported Fire Ant?
Single queen (monogyne form): only one queen per colony or mound; slightly larger workers; members of colonies are territorial; mound densities usually 20 to 80 mounds per acre; and overall fewer ants per acre. Multiple queen (polygyne form): dozens of queens per colony; smaller size worker ants; colonies are interconnected; mound densities 100 to 1,000+ per acre, therefore more ants per acre. All colonies found in California to date have had multiple queens.

How can I tell the difference between Red Imported Fire Ants and termites?
Although most Red Imported Fire Ants are recognizable as ants, virgin queen and male Red Imported Fire Ants with wings could be confused with termites, especially when termites are flying during their mating periods. The front pair of wings on Red Imported Fire Ants is larger than the hind pair, while both pairs of termite wings are approximately the same size. Red Imported Fire Ants have bent ("elbowed") antennae and a thin ("wasp-like") waist, very narrow between the middle (thorax) and hind (abdomen) segments. Termites have straight, hair-like antennae, and the middle and hind segments of the termite worker's body are broadly connected at the waist.

Comparison of Red Imported Fire Ant and termite Graphic courtesy of the UC Davis Statewide Integrated Pest Management Project. (Please click on graphic for a full size view.)