This is a high mountain species, found rather commonly in the Alps, the Pyrenees and the Picos de Europa. Curiously, Kudrna (2015) counts all the Pyrenean records as being of the closely related Gavarnie blue, Plebejus pyrenaicus. I have looked in vain for this latter species in the Val d'Aran, my own Pyrenean haunt, and never confirmed it. All the individuals shown above as from Spain were from the Val D'Aran. So far as I can see, all other books recognise that glandon blues fly in the Pyrenees.

The male glandon blue is readily identified. He is a small butterfly, rather dull, silvery blue above, suffused with dark scales and with dark margins. The discal points on all wings are pronounced and usually edged in a paler colour. The female is similar but all brown above. Both sexes have a cell spot on the underside of the forewing. The discal spot on the underside hindwing is usually all white, with no black pupil, and other spots may also be blind, especially in the female. The Gavarnie blue, found more locally in the Pyrenees, is lighter above and beneath, with mostly blind spots on the hindwing underside and a largely white border to the underside. Populations of glandon blue from the south of Spain are now recognised as of a separate species, Plebejus zullichi, and eastern European Gavarnie blues are now recognised as being a further species, Plebejus dardanus. Northern Scandinavian populations of glandon are currently treated as another distinct species, Plebejus aquilo.

The foodplants are various species of Androsace, depending on location and altitude. The glandon blue hibernates as a small larva.