Several species of ants have a special symbiotic relationship with aphids- they farm them! Aphids feed primarily on the sap from plants and secrete a liquid called honeydew. This secretion is very sugar-rich, and quite favoured by ants as a food source.
As a result, a system has been hashed out by these insects wherein the ants herd the aphids around to the juiciest parts of plants, protect them from predators, and carry them into their nests at night and for winter. In return they are allowed to ‘milk’ the aphids- stroking the aphids with their antennae, coaxing them to secrete their honeydew which is then lapped up by the ant.
