The learning capacity of ants is rigidly limited, however, and in contrast to mammalian learning is stereotyped and restricted. Many ants function only through subterranean galleries, many are strictly arboreal, but commonly the species range both above and below the surface of the earth. Communication among ants is highly efficient and is conducted mainly through tactual and chemical means, although some species exhibit vibratory and even auditory processes. For example, in the diminutive reddish-yellow Pharaoh ant, common in kitchens, the excited finder, in returning to the nest, releases a track of chemical secretion that directs others to the food. Usually the excitement of the finder is greater when larger concentrations of food are discovered, and thus correspondingly greater numbers of nestmates are stimulated to forage.
Many ants live as temporary or permanent social parasites in the colonies of other ant species.
The Amazon ant carries out forays against other ants and brings back to the home nest some of the unconsumed brood to serve as slaves when mature. These slave ants perform the work of the Amazon colony, including excavation and brood-tending. The large mound communities of this pest disrupt mechanized farming and damage crops. The tiny black ant and its close relative, the sugar ant, infest households in the United States. In the northern states the carpenter ant is another common intruder around dwellings.