Thatching ants are medium to large ants (3/16 – 5/16 inch long). They can be black to red and black. These ants are sometimes called mound ants because some species construct mounds from plant debris like fir needles. Thatching ants sometimes nest in decayed logs and rarely in wall voids of homes. Their normal pest status comes from nesting in landscapes where physical contact becomes inevitable. When their mounds are disrupted by human contact they bite in mass and then spray the area with formic acid to produce a painful sensation. They are fierce predators and should be protected whenever possible. Mating swarms occur in late summer to early fall.