Pyrgus alveus

ssp. centralhispaniae, Val d'Aran.

centralhispaniae

Male, Switzerland, May 2007 (ssp. alveus)

Male, Switzerland, May 2007

Male, Switzerland, May 2007

Male, Switzerland, June 2006

alveus

alveus
In Switzerland, the combination of large size, small spots, rather diffuse but present markings on the upperside hindwing and the absence of specific characters for other species (!) combine to make identification generally possible and often confident.
The butterfly flies in my garden from May onwards and later at higher altitudes.