Butterfly

Aphids are tiny sap-sucking bugs. Plant sap is an unbalanced diet for Aphids as it lacks essential amino acids, Which aphids, like all animals, can not Synthesise, and possesses a high osmotic pressure due to its high sucrose concentration.
Some species of ants "farm" Aphids, protecting them on the plants they eat, eating the honeydew that the Aphids release from the terminations of their alimentary canals. This is a "mutualistic relationship".
These "dairying ants" "milk" the aphids by stroking them with their antennae.
An interesting variation in ant–aphid relationships involves lycaenid butterflies and Myrmica ants. For example, Niphanda fusca butterflies lay eggs on plants where ants tend herds of aphids. The eggs hatch as caterpillars which feed on the aphids. The ants do not defend the aphids from the caterpillars but carry the caterpillars to their nest. In the nest, the ants feed the caterpillars, which produce honeydew for the ants. When the caterpillars reach full size, they crawl to the colony entrance and form cocoons. After two weeks, butterflies emerge and take flight