''Phengaris alcon'', more commonly known as Alcon Blue or Alcon Large Blue, is a butterfly of the Lycaenidae family and is found in Europe and Northern Asia.
It can be seen flying in mid to late summer. Like some other species of Lycaenidae, its larva stage depends on support by certain ants; it is therefore known as a myrmecophile.
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.. more