Polyommatus eros

Eros blues with glandon blues and silver-studded blues, July 2005, Val d'Aran

July 2005, Val d'Aran

Switzerland July 2001

Distribution

The Eros blue was formerly considered as two species: eros (in the Alps, Pyrenees, Apennines, Carpathians and the Dinaric mountains) and eroides, the 'false Eros blue' (in the Balkans and eastern Europe). Most modern books treat these as subpsecies of the same species. It is strictly a high mountain butterfly, as its distribution suggests, though I have seen it as low as 600m where regular avalanches and landslips bring alpine soil and plants lower down. This is generally a common butterfly in Switzerland, fond of gathering with other blues at damp spots to take minerals. It flies in a single brood from June through to August or September.

The upperside of the male is gleaming, pale sky blue, with a characteristic reflective sheen. The margins on both wings are relatively broad - 'felt tip' rather than drawing pen. The underside is very similar to that of the common blue, a close relative. Like the common blue it has a cell spot in the forewing. The female is brown above with variable amounts of blue at the base of the wings. This blue, like that of the male, has a characteristically silvery, reflective feel, making her quite distinctive.

The larval foodplants are Oxytropis halleri and O. campestris in the west, and Genista depressa in the east - subspecies eroides. The larvae, like those of most blues, are attended by ants. They hibernate while small.