Alcon Blue

Reproduction

The butterfly lays its eggs onto the Marsh Gentian; in the region of the Alps they are sometimes also found on the related Willow Gentian. The caterpillars eat no other plants.

Alcon larvae leave the food plant when they have grown sufficiently and wait on the ground below to be discovered by ants. The larvae emit surface chemicals that closely match those of ant larvae, causing the ants to carry the Alcon larvae into their nests and place them in their brood chambers, where they are fed by worker ants and where they devour ant larvae.

When the Alcon larva is fully developed it pupates. Once the adult hatches it must run the gauntlet of escaping. The ants recognise the butterfly to be an intruder, but when they go to attack it with their jaws they can't grab anything substantial as the newly emerged adult butterfly is thickly clothed in loosely attached scales.

Over time, some ant colonies that are parasitized in this manner will slightly change their larva chemicals as a defense, leading to an evolutionary "arms race" between the two species.

Generally, Lycaenidae species which have a myrmecophilous relationship with the ant genus "Myrmica" are locked to primary host specificity.
The Alcon Blue is unusual in this regard in that it uses different host species in different locations throughout Europe. It is known to use "Myrmica scabrinodis", "Myrmica ruginodis", and "Myrmica rubra" as the primary host within differing European zones.

Predators

The "Phengaris alcon" larvae are sought underground by the "Ichneumon eumerus" wasp. On detecting a "P. alcon" larva the wasp enters the nest and sprays a pheromone that causes the ants to attack each other. In the resulting confusion the wasp locates the butterfly larva and injects it with its eggs. On pupation, the wasp eggs hatch and consume the chrysalis from the inside.