What are red imported fire ants? What makes them different from Texas native ants?

Red imported fire ants or Solenopsis invicta are medium-sized red and black colored ants that build mounds of soft soil. Mounds are rarely larger than 18″ in diameter. In cold, dry areas such as the High Plains of Texas, mounds are usually much smaller and harder to detect. When disturbed, fire ants emerge aggressively, crawling up vertical surfaces, biting and stinging “all at once”. Their sting usually leaves a white pustule on the skin. Worker fire ants vary in size from small (1/16 inch) to large (almost ¼ inch) in length. Many native ant species have worker ants that are uniform in size and may vary in body color. Other small to medium-sized ants that build small nests in soil often have central nest openings through which the ants enter and leave whereas fire ants mounds have no central openings.

Harvester ants are much larger and make large bare areas with a single entrance hole to the colony.

Leafcutter ants are also much larger and have a distinctive built-up dense cluster of mounds at the colony’s center called a “town”, and have many entrance holes over a very large area.

Can I tell the difference between fire ants and native ants? How large are fire ants?

Some uncertainty comes from the fact that red imported fire ants vary in size (1/16 to almost 1/4 inch long – see image by S. D. Porter, USDA-ARS), with the largest workers 2 or 3 times larger than the smallest. Red imported fire ants are an exotic invasive species and in many areas of Texas they have displaced other species of fire ants native to the state.  Solenopsis geminata, the tropical fire ant, is the most common native fire ant species encountered. To the unaided eye, they are almost identical to red imported fire ants. However, S. geminata will have a few larger workers with large, square-shaped bi-lobed heads. These ants specialize in collecting and milling seeds, but build mounds similar to red imported fire ants.

 

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