The red imported fire ant (Solenopsis invicta) is an invasive species known for its aggressive nature and painful, burning sting. This pest has established a firm and disruptive presence across the southeastern United States, impacting local ecosystems, agriculture, and human health. The arrival of the fire ant in Texas is a relatively recent phenomenon, marking a significant change in the state’s natural landscape.
Where Fire Ants Originated
The red imported fire ant is native to the tropical areas of central South America, specifically the low-lying floodplains of the Paraná River basin, encompassing parts of Argentina, Paraguay, and Brazil. In their native South American habitat, fire ant populations are naturally kept in check by a diverse array of competitors, predators, and pathogens. These natural enemies include various species of parasitic phorid flies and a microsporidian pathogen, which together exert pressure on the fire ant’s ability to thrive unchecked. When the ants were accidentally transported to the United States, they arrived without these biological controls. The absence of these regulators allowed the species to explode in density and aggressively dominate the new environment.
The First US Foothold and Texas Entry
The initial arrival of Solenopsis invicta in North America is traced back to the seaports along the Gulf Coast, with the first colonies established in the 1930s, likely through the port of Mobile, Alabama. They are believed to have arrived in the soil used as ship ballast or within imported plant nursery stock from South America. After establishing a foothold in Alabama, the ants began expansion across the Gulf Coast states. The first documented appearance in Texas occurred in the southeastern part of the state, likely around the Beaumont or Houston areas, in the early 1950s. This sighting confirmed the species had successfully crossed the Louisiana border and was poised to spread across the Texan landscape.
How Fire Ants Spread Across the South
Following their initial entry into Texas, the fire ants rapidly expanded their range through a combination of natural and human-assisted transport methods. One significant natural dispersal mechanism is the nuptial flight, where winged reproductives fly to mate, with mated queens traveling miles before establishing a new colony. Another natural vector is the colony’s ability to form a living raft when faced with rising floodwaters, allowing the entire colony to float to new land.
However, the rapid long-distance spread is largely attributed to human commerce, as the movement of contaminated materials, such as potted plants, sod, hay, and agricultural equipment, has effectively bypassed natural barriers. Mated queens also land on vehicles, including cars, trucks, and trains, hitching rides that carry them hundreds of miles beyond the species’ natural expansion.
Present Day Range and Identification
Today, the red imported fire ant has infested the eastern two-thirds of Texas, with its range extending north and west until limited by insufficient moisture and prolonged freezing temperatures. The current range covers virtually all of the state’s high-rainfall and irrigated areas, with the western boundary generally following a line from the Panhandle south to the Rio Grande. While less common in the drier Trans-Pecos regions, their territory continues to expand in suitable habitats.
The most conspicuous sign of their presence is the characteristic dome-shaped mound they build, which can be up to 18 inches tall in open, sunny areas. Unlike mounds built by native ants, the fire ant mound does not have a central opening; workers access the nest via subterranean tunnels. Disturbing the mound will elicit an aggressive, immediate defensive response, with hundreds of workers swarming the surface and inflicting multiple stings.