The sloe hairstreak is widely distributed across Europe but generally rather local. I know of several sites in Switzerland where it is supposed to fly but have only actually seen it at one. There, it is in fact very common. The species likes grassy areas with copious sloe bushes and plenty of sun.

Identification is not a problem, given a good view. Most obviously, the orange lunules on the hindwing are confluent, forming something closer to a band than a series of spots. They may enclose a blue spot near the anal angle but this is neither as large nor as deep blue as in blue-spot hairstreak. The butterfly is also smaller than that species and the hairstreak is less bold. Like many other Satyrium species, sloe hairstreaks enjoy sitting on umbelliferous plants like yarrow, though they also enjoy the privet that grows among the sloe bushes.

The female sloe hairstreak has a brush of black hairs on her abdomen, some of which she carefully transfers to each egg she lays, rendering it much less visible than it would otherwise have been. This shaky video - I tried not to approach too close - shows one doing just this: