I see huge numbers of these butterflies in those parts of the countryside where its main food plant, Lotus corniculatus (Bird's-foot Trefoil) grows. If that is in shortish grassland then you can easily spot the pupae attached to grass stems. The male is blue but the female varies in colour in the British Isles being mostly brownis blue in the South and quite blue in Scotland.

On the continent the female blue can be so well marked with the orange on the upper wing that at first it looks like a different species. The RHS photo is of a female taken in Andalucia, Spain.

LHS and Mid: Newborough Warren 29th May 2008 RHS: Near El Burgo , Spain 31st March 2008

Added on 25th June 2008