| Family | Lycaenidae |
|---|---|
| Subfamily | Polyommatinae |
| Genus | Phengaris |
| Species | alcon |
| Authority | ([Denis & Schiffermüller], 1775) |
| English Name | Alcon Blue |
| European Red List 2010 | Least Concern (LC) |
|---|---|
| EU 27 Red List 2010 | Near Threatened (NT) |
| European Red List 2025 | Near Threatened (NT) |
| EU 27 Red List 2025 | Near Threatened (NT) |
| Habitats Directive | |
| Bern Convention | |
| CITES |
The Alcon Blue occurs in local, scattered populations. Oftentimes it is referred to as two distinct species: P. alcon on low-lying wet heathland, on moist fen meadows and bogs, and P. rebeli on dry as well as sub-alpine calcareous grasslands. Usually, only a few butterflies are seen. The bright, white eggs are easy to find. Depending on the habitat, they are laid on the flowers and sepals of Marsh Gentian (Gentiana pneumonanthe), Willow Gentian (G. asclepiadea), and Cross Gentian (G. cruciata). At first, the small caterpillars feed on the ovaries of the foodplant, but they pass the last instar in the nests of various Myrmica ants, which they parasitize by living like young cuckoos, being fed by the worker ants. They hibernate and pupate in the ant nests. The Alcon Blue has one generation a year.
Albania / Andorra (Regionally Extinct) / Austria / Belarus / Belgium / Belgium: Flanders / Belgium: Wallonia / Bosnia and Herzegovina / Bulgaria / Croatia / Czechia / Denmark / Estonia / France / France: Mainland / Germany / Greece / Greece: Mainland / Hungary / Italy / Italy: Mainland / Latvia / Liechtenstein / Lithuania / North Macedonia / Montenegro / Netherlands / Poland / Portugal / Portugal: Mainland / Romania / European Russia / Serbia / Serbia: Serbia / Serbia: Kosovo / Slovakia / Slovenia / Spain / Spain: Mainland / Sweden / Switzerland / Ukraine /