A fire ant mound begins as a small cell a few inches deep in the ground where the queen seals herself in to begin the colony. As workers are produced, they begin to tunnel into the surrounding soil, making many interconnected chambers. The soil removed during the formation of the chambers and tunnels is carried above ground where it is used to form many more chambers and tunnels.
A mature colony (a year or so old) consists of a mound - a conically shaped dome of soil - that may be 1 or 2 feet in diameter and 1 to 1-1/2 feet high. The average mound is 15 inches in diameter and 10 inches high. In low marshy terrain, mounds may be 3 or more feet high and up to 3-1/2 feet in diameter.
During the hot dry months of summer, the ants do not maintain their mounds, and they may be easily overlooked. However, as soon as rains and cooler weather return, the mounds are reworked and become quite noticeable. The mound surface usually has a slight crust that protects it. The inside of the mound is filled with tunnels and chambers. These chambers form a cone which extends 1 to 3 feet into the ground. Some of the tunnels may extend down 5 feet or more depending on the water table. Most mounds have no visible entrances or exits except during mating flights. At these times, the workers open numerous holes on top of the mound. They promptly close the holes after use. The workers leave and return to the mound in lateral tunnels just under the soil surface that radiate out from the mound. These shallow tunnels are 1 to 4 inches underground and may extend many yards from the mound. They may branch, and at points along their length are openings that lead to the surface from which the ants emerge to forage.
The preceding article is courtesy of the Texas Department of Agriculture.