Diagram of a fire ant mound
One of the identifying characteristics of a fire ant colony is its earthen nest or mound. The mound is a conical (cone-shaped) dome of excavated (dug up) soil. The mound begins as a small cell, like a small room, a few inches deep in the ground, where the newly fertilized queen seals in herself to begin her colony.
A mature fire ant colony (a year or so old) consists of a mound averaging 12 to 15 inches wide and about 10 inches tall. The mound’s size and shape differs to some extent from other mounds based on soil type.
The surface of a fire ant mound usually has a slight crust that protects it. The inside of the fire ant mound is filled with tunnels and chambers. These chambers form a cone that extends 1 to 3 feet into the ground. Some tunnels may extend downward 5 or more feet, depending on the water table.
Most fire ant mounds have no visible entrances or exits except during mating flights. At mating time, the workers open many holes on top of the mound. The holes are closed promptly after use.
Read more about fire ants at eXtension.org.