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 small pieces of plant material. The number of adult workers per colony may be as high as 40,000. The size of these mounds in highly variable and dependent on the age and health of the colony. The height of the average mound ranges from 1 inch (1.5cm) to 18 inches (45.7cm), although nests of larger heights are not uncommon. Nests can extend up to 4 feet (1.2 meters) into the ground. When their mounds are disrupted by human contact they bite and then spray the area with formic acid they produce.