Capture a suspected fire ant in a jar or place one on a piece of paper. Observe the ant closely. A fire ant has a dark, reddish-brown color on most of its body and head. However, the abdomen appears darker in color. Although the size of regular ants varies by species, fire ants are generally about one-sixteenth to one-fifth of an inch long.
Search the yard for an ant hill or mound. Unlike regular ants, which typically build low-lying nests, fire ants have mounds as high as 15 inches. The mounds are also often 15 inches in diameter and can go as deep as five feet into the ground.
Watch the ants' behavior. Fire ants become aggressive if the mound or nest is disturbed. Regular ants do not normally act as aggressively.
Check arms and legs for any ant bites. A bite from a fire ant can be painful and grow into a small welt.