There are several species of fire ant. However, the two species which invade new areas are the Imported Fire Ants (IFA). The IFA were introduced into the United States from South America at the port of Mobile, Alabama. The black imported fire ant, Solenopsis richteri Forel, arrived around 1918 and the red imported fire ant, Solenopsis invicta Buren is considered the worst and believed to be introduced into the U.S. in the late 1930’s. Both species probably came to the port in soil used as ballast in cargo ships.
Today, IFA infest more than 367,000,000 acres in Alabama, Arkansas, California, Florida, Georgia, Louisiana, Mississippi, New Mexico, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia and Puerto Rico. They are discovered sporadically in Maryland.
Fire ants cannot eat solid food, so they carry it back to the nest and feed it to the oldest larvae, which are able to externally digest solids and turn them into nutritious liquids. The worker ants then share this now-edible byproduct with the queen and the rest of the colony.
Fire Ant Mounds
Fire ant mounds do not have an opening at the center like other ant mounds. Imported fire ants use underground tunnels which radiate from the mound. Another characteristic of the mound is the soil appears to be fluffy and worked, especially a few days after a heavy rain. When the soil is compact the tunnels become visible on the surface. Mounds in clay soil are usually larger than in sandy soils. Mature colonies may contain up to 500,000 ants.
If there is a lack of surface water, the ants tunnel down to the water table for the cooler environment and water. Of course this gives the appearance that the mounds have disappeared. After a heavy rain the ants will move upward for the dryer and warmer environment. In grass the mounds may reach just a few inches tall but undisturbed mounds can reach up to 24+” in height. I have personally seen fire ant mounds in Texas which were approximately 24” tall and 2+ feet wide. Other areas fire ants build their mounds are around objects such as stumps, rotting logs, fence rows, trees and under structures.