This is perhaps one of the most beautiful species of butterfly of all, the male with a range of hues of the most wonderful sky blue imaginable. 

The chequered black and white fringes are helpful in distinguishing it from other species on the wing at the same time, and I have encountered it both on Downland in the South of England, and in the Alps, where it is much more common. 

The female, butterfly photo on the left here, has a variable amount of blue, this particular one exhibiting quite a lot more than average. 

Anyone who appreciates butterflies should make an effort to see this species on the wing, they won't be disappointed.