Ants are one of the few groups of animals which modify their immediate environment to suit their needs. They build often elaborate nests in a range of situations, sometimes expending huge amounts of energy in their construction. These nests are commonly occupied for years and some for decades. In addition, some ants use plant fibres or soil to construct protective coverings over nests and feeding areas. Only a handful of animals manufacture such elaborate and complex structures.
Nests in soil vary from small, simple chambers under rocks, logs or other objects on the ground to extensive excavations extending a meter or more into the soil. The exact structure of the nest varies with the species, soil type and situation. The entrances to these subterranean nests show a wide range of styles. Many are no more than a cryptic hole just large enough for a single worker to squeeze through. Others are a single entrance surrounded by soil which varies from a low and broad mound to a tall, narrow turret. A number of species assemble soil and leaves around their nest entrances to form large piles with well-defined, vertical sides and concave tops. Others collect plant material to construct thatched mounds above their subterranean nests.
A nest of the sugar ant, Camponotus consobrinus, often have a simple entrance surrounded by a low mound of loose dirt. Several queens are just leaving this nest to mate and establish nests of their own.
Only a handful of Australian ants use thatch when constructing their nests, including this Iridomyrmex species.
Most ants nest in soil with a low mound of loose dirt at the entrance, such as this Myrmecia species.
Some species disperse soil removed during nest construction, leaving little indication of the entrance other than a small hole, as in this Iridomyrmex discors nest.
The nests of the common meat ant of south-eastern Australia (Iridomyrmex purpureus) can grow to enormous sizes with tens of thousands of workers. They clear all vegetation from the surfaces of their nests and cover them with small stones. A single colony can be composed of numerous individual nests separated by up to several hundred metres. Individual nests can have 10 or more separate, small entrances just large enough for individual workers to move through.
A large nest of I. purpureus. Nests can contain up to several hundred thousand workers.
A well-worn highway connects two nests within a colony of I. purpureus.
Some species of ants nest arboreally. Their nests are most frequently found in twigs, branches or the trunks of trees. Australian species are not known to attack firm wood, most utilising the burrows of other insects such as beetle larvae, or entering rotten wood or wound sites caused by wind or insect damage. In most cases the entrances to these types of nests are either small and circular or are formed by the natural contours of the tree or branch.
An arboreal nesting Crematogaster species, including the large queen and much smaller worker.
In a few arboreal species nests are constructed using leaves. For example, the green tree ant (Oecophylla smaragdina) stitches together individual leaves with silk produced by their larvae. The colony expands both by enlarging existing leaf nests and by adding new satellite nests. In other arboreal species, plant fibres are used to construct coverings which are attached to the surfaces of leaves. The ants live within the chamber formed by the covering and leaves.
The Green Tree Ant, Oecophylla smaragdina, forms nests by stitching leaves together using silk produced by their larvae. Normally the exterior of the nest is quite, but in this case the nest has been disturbed and workers have pored forth to determine the nature of the intruder.
While many ants form elaborate nests, those of other species are relatively simple. Many of the species found in rotten wood do little more than remove loose wood fibres to construct simple chambers for workers and brood. These chambers can be small or very extensive but often lack the complexities of nests found in soil or arboreally. Finally, a handful of species (for example some Leptogenys) lack what would normally be thought of as a nest and are found in small groups clustered on the ground in leaf litter or among the roots of plants. These species move their "nests" frequently and can be found in a wide range of suitable sites.