More on Aphid-milking Ants…

Some species of ants ”farm” aphids, protecting them on the plants they eat, and 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.^[11][12] Therefore, sometimes aphids are called “ant cows”.

Some farming ant species gather and store the aphid eggs in their nests over the winter. In the spring, the ants carry the newly-hatched aphids back to the plants. Some species of dairying ants (such as the European yellow meadow ant, Lasius flavus)^[13] manage large “herds” of aphids that feed on roots of plants in the ant colony. Queens that are leaving to start a new colony take an aphid egg to found a new herd of underground aphids in the new colony. These farming ants protect the aphids by fighting off aphid predators.^[12]

An interesting variation in ant-aphid relationships involves Lycaenid butterflies (such as the Sievers blue butterfly and the Japanese copper butterfly) and the 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.^[14]

Some bees in coniferous forests also collect aphid honeydew to make “forest honey”.^[8]

Many aphids are host to endosymbiont bacteria, Buchnera, inside specialized cells called bacteriocytes. These bacteria synthesize some essential amino acids that are absent from the phloem that the aphids eat.^[15]

(from Wikipedia)