The Black Hairstreak is a very localised butterfly occurring in only a small number of colonies across the south and east Midlands generally, and is recorded at only one site in Leicestershire within the three counties which make up the East Midlands Region of Butterfly Conservation. It favours dense stands of mature Blackthorn in sheltered, sunny locations along woodland edges. In common with other hairstreaks it spends much of its time high in the canopy of large trees, but will come down to nectar on bramble flowers and Wild Privet.
Both sexes are similar, and can be easily confused with the White-letter Hairstreak. The main distinguishing feature is the row of black and white tapering spots above the orange band on the underside of the hindwings, and the white 'W' is less pronounced.
The flight period is very short between mid-June and early July.