Iolana iolas - Iolas Blue 

Iolana-iolas-iolas-blue | PTKbutterflies
Iolana-iolas-iolas-blue | PTKbutterflies
Iolana-iolas-iolas-blue | PTKbutterflies

I have seen this species only once, and then only males, very close to Bladder Senna, the larval food-plant in the Valais of Switzerland.. 

They are a very large Blue comparatively and I was fortunate, despite their activity, I had a couple of moments for butterfly photography.