The field ant is a very large group of ants, making up a sixth of the ant population. They generally make their nests in mounds outside, but have been known to enter houses in search of food. Field ants are fairly good sized, around 1/4" long, ranging in color from brown, to black, to red. It's typical to see these ants around cracks in the concrete, or you may see large numbers of light brown swarmers in the fall.