The role of Ants

The Silver-studded Blue (Plebejus argus) depends on ants for the satisfactory completion of its life-cycle. This is described as a myrmecophilic relationship. Eggs are deposited close to the ground in areas frequented by ants, sometimes on plants that the larvae can eat, but also on bracken and under stones, where they lie until the following winter. The main larval host plants are heather, bird’ s-foot trefoil and gorse, but only tender “ pioneer ” shoots are eaten. The young larvae are found and tended by ants of a few species within the genus Lasius. Lasius psammophilus (formerly referred to as L. alienus), nests all over the common, but particularly where vegetation is sparse and sunlight reaches the ground. L. niger is also present, but in lesser numbers. The ants are attracted to a sweet substance, which the larva secretes from a honey gland on its back. The presence of the ants protects the larvae from predators, notably parasitic wasps, and their reward is the honey. When the larvae are ready to pupate, they are accompanied underground by the ants, usually into an ants nest. They do not eat the ant grubs in the way of the Large Blue, but benefit from continued protection until they are ready to hatch. Their chances of surviving a fire on the heath are much improved whilst below ground. The adult butterfly emerges from its chrysalis in late June, and crawls out of the nest in the company of a cluster of ants, giving it continued protection during the period of vulnerability whilst it dries its wings for flight.

Larva of P. argus attracts black ants of Genus Lasius