Spialia sertorius - Red-underwing Skipper
This is the first of the few Spialia genus I have seen. The species tend to have a submarginal band of small spots on both fore and hindwing uppersides. The Red Underwing Skipper has indeed that... a Red Underwing. Quite beautiful. It is a tiny but very busy butterfly, difficult to photograph and always a joy to behold, as it is quite easy to overlook.
It flies, not uncommonly, in Western Europe.