[IMAGE 1 of 2] An Atta mexicana
nest/colony can have dozens of entrances. Some tunnels can run underground for 60 m / 67 yards or more, and emerge close to a reliable source of leaves. Multiple entrances have also been shown to provide ventilation for the sometimes enormous underground nests. Especially in younger, rapidly growing colonies, new subterranean galleries and tunnels are constantly being added, and expanded. The excavated soil from all of this digging is brought to the surface and dumped - resulting in volcano-like craters up to approx. 30 cm / 1 ft in height, with entrance holes in their centers (older colonies that are not expanding may show little to none of the these external surface craters - their entrance holes being unadorned, and sometimes difficult to spot). Most of these soil-excavating duties appear to be carried out by the smaller media, and minor workers. As can be seen in this image, the soil is usually moist and clumped when brought up from below (making it very easy to transport), but dries quickly when exposed to the sun and air. Note: in addition to excavated soil, Atta mexicana
(and some other Atta
species) also bring to the surface and dump the organic refuse from their underground fungus-garden chambers.