Mazarine Blue Cyaniris semiargus
There were at least three species of blue butterfly flitting between the plants and each other on this warm day in the hills. I had thought I'd photographed both upper wings and underwings of this butterfly but the uppers were all of the Turquoise blue (Plebicula dorylas) which to me as an inexperienced butterfly hunter looked very similar. This butterfly is no longer found in the UK but is found over most of southern, mid and northern Europe even as far north as the Arctic Circle. The female has brown upper wing colours while both sexes slightly resemble Cupido minimus (Small Blue) in their under wing markings.
The main larval food plant is Trifolium pratense (Red Clover) and one theory for the extinction in Britain is that hay is cut too soon before the pupa stage. Unlikely though isn't it? Trifolium pratense is and always has been one of the commonest plants in the UK even present on the outer Hebrides and St. Kilda and only a fraction of the countryside has ever been dedicated to haymaking.
Hills opposite Gèdre, French Pyrenees, 13th June 2009
Added on 14th June 2010