This little butterfly is called purple hairstreak (Neozephyrus quercus), eikenpage in Dutch. They are quite rare in my region of The Netherlands, mainly because they are picky about their habitats.
These butterflies like to dwell high up in oak trees, and they prefer to eat from the blossom of buckthorn (Rhamnus), vuilboom in Dutch.
This tree-loving behaviour makes them a pain to photograph, but I managed to take some shots a few days ago:
Olympus Stylus 1s, 300mm, ISO200, f5.6, 1/250s
Olympus Stylus 1s, 300mm, ISO200, f5.6, 1/200s
Sorry for the clipping of the lightest bits; it couldn't be helped.
Thanks for watching!