The harvesting habits of certain ants have long been known, the subterranean store-houses of Mediterranean species of _Aphaenogaster_ having been described by J.T. Moggridge and A. Forel, and the complex industries of the Texan _Pogonomyrmex barbatus_ by H.C. McCook and W.M. Wheeler. The colonies of _Aphaenogaster_ occupy nests extending over an area of fifty to a hundred square yards several feet below the surface of the ground. Into these underground chambers the ants carry seeds of grasses and other plants of which they accumulate large stores. The species of _Pogonomyrmex_ strip the husks from the seeds and carry them out of the nest, making a refuse heap near the entrance. The seeds are harvested from various grasses, especially from _Aristida oligantha_, a species known as "ant rice," which often grows in quantity close to the site selected for the nest, but the statement that the ants deliberately sow this grass is an error, due, according to Wheeler, to the sprouting of germinating seeds which the ants have turned out of their store-chambers.
Perhaps no ants have such remarkable habits as those of the genus _Atta_,--the leaf-cutting ants of tropical America (fig. 2, 1). There are several forms of worker in these species, some with enormous heads, which remain in the underground nests, while their smaller comrades scour the country in search of suitable trees, which they ascend, biting off small circular pieces from the leaves, and carrying them off to the nests. Their labour often results in the complete defoliation of the tree. The tracks along which the ants carry the leaves to their nests are often in part subterranean. H.C. McCook describes an almost straight tunnel, nearly 450 ft. long, made by _Atta fervens_.
Within the nest, the leaves are cut into very minute fragments and gathered into small spherical heaps forming a spongy mass, which--according to the researches of A. Möller--serves as the substratum for a special fungus (_Rozites gongylophora_), the staple food of the ants. The insects cultivate their fungus, weeding out mould and bacterial growths, and causing the appearance, on the surface of their "mushroom garden," of numerous small white bodies formed by swollen ends of the fungus hyphae. When the fungus is grown elsewhere than in the ants' nest it produces gonidia instead of the white masses on which the ants feed, hence it seems that these masses are indeed produced as the result of some unknown cultural process. Other genera of South American ants--_Apterostigma_ and _Cyphomyrmex_--make similar fungal cultivations, but they use wood, grain or dung as the substratum instead of leaf fragments. Each kind of ant is so addicted to its own particular fungal food that it refuses disdainfully, even when hungry, the produce of an alien nest.