Mountain Alcon Blue

Maculinea rebeli

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Male, Switzerland, June 2005

Female, July 2007

Female, Switzerland, July 2005

Male underside, Switzerland, June 2005

Female ovipositing, Switzerland, June 2005

The same female

It has taken me a long time to find an amenable colony of this mountain butterfly. It is generally local and sporadic, though at the location where these pictures were taken it was actually reasonably abundant. The female shown above is clearly laying eggs on some species of gentian - probably Gentiana cruciata, though I will have to check this up. The males were conspicuous by their size and apparent 'weight' in flight, though at rest they do not seem huge at all. Almost all individuals were flying at one location, which was an extended corner of a high alpine pasture, grazed by cattle. One or two males were to be found further away along a flowery bank.

The butterfly is easily separated from most European blues by the combination of large size, typical Maculinea underside, the bright, unmarked upperside of the male with a broad dark border and the absence of a cell spot on the forewing underside (this separates it from large blue, though that does frequently also lack the spot at altitude). The alcon blue, of which I have no photographs, is similar, but lacks any blue scaling at the base of the underside hindwing, has very slightly narrower borders on the upperside of the male and no blue on the female (there is considerable blue at the base of the wings in mountain alcon blue). Alcon also generally flies below 1000m while mountain alcon prefers altitudes well above this. It is extinct in Belgium, where it presumably used to fly at low altitudes...