Cupido minimus - Small Blue
This charming tiny butterfly is very common in the Alps, but less so in the UK where I have to travel distances to either East or West coast to see it. As it's name suggests it is small, but some can approach the size of the Common Blue!
The male butterfly shows varying amounts of blue upper-side scaling and the females though lacking blue scales, can sport a very attractive blue iridescent sheen.
It was a long time before I found it in the UK, and I still enjoy achieving a good photograph of this species.