A few species have developed highly specialized agricultural or pastoral habits. The red harvester ant of the central United States and Mexico frequents fields of grass, harvesting and storing the grass seeds. Some species of the widely distributed harvester ants, which gather grain for food, have developed specialized workers, sometimes called soldiers, with enlarged jaws, and these soldiers do virtually nothing but crack the seeds for the other ants to eat. A genus of ants of the southeastern United States and tropical America cultivate inside their nests a species of fungus that is used as food by the colony. The tropical American species are called leaf-cutting ants because the workers cut off pieces of leaves, which are carried back to the nest and used to fertilize the fungus gardens.
Many ants eat a sweet fluid, called honeydew, that is excreted by aphids.
Some species actually keep and protect the aphids and care for their eggs. Honeypot ants of the southwestern United States store honeydew, utilizing certain workers as living containers for the fluid. They remain motionless in the nest, disgorging droplets of food as required to feed other members of the colony. Many ants practice trophallaxis, which involves complex forms of reciprocal feeding and the exchange of chemical stimulation. While feeding the larvae, the worker ants obtain from the surface of the larvae's bodies a salivary secretion that the workers eat avidly.