Spotting

Or maybe Polyommatus amandus.

Might be a male Polyommatus damon, or perhaps Lysandra bellargus.
The western tailed blue is an american species, and not likely to be found in Slovenia, I think.

Certainly not a Western tailed-blue. The Western tailed-blue (Cupido amyntula) is a North American species. Also, although there European lycaenids with tails are the butterfly in these pictures here has no tails :-)

Thanks! I will try next time :)

It might be a Western tailed blue but I agree the determining factor would be the underside but unfortunately you couldn't get a shot ( Awesome Photos )

Thanks!
Unfortunately, I don't have any underside view... it was too quick.

Hi Irena! Lycaenidae. Any underside view?