The Black Hairstreak (Satyrium pruni) is one of the rarest and most elusive butterflies in Britain. It is also one of the most recently discovered (1828), due to the similarity with its close cousin, the White-letter Hairstreak (Satyrium w-album).
S. pruni is not a great wanderer and an entire colony will often restrict itself to a single area within a wood, despite there being suitable habitat nearby. This inability to colonise new areas at a pace, in balance with habitat loss, may partially explain the scarcity of this species. This butterfly has a very restricted distribution that is confined to a line of clays between Oxfordshire in the south-west and Cambridgeshire in the north-east. Colonies are typically located in small woods or nearby hedgerows, where blackthorn, the main larval foodplant grows. Sites are located in sheltered but sunny positions and typically have a southerly aspect to them.
The adult stage has an extremely short flight period, being typically seen in the last two weeks of June and the first week of July. There is a single generation each year. Upon emergence, the adults spend much of their time resting high up on maple, ash or the larval food-plant, crawling over leaves and twigs, in search of aphid honeydew from which they feed. Primarily an arboreal species they will occasionally come down to feed on various nectar sources including man made attractants. As with all hairstreaks, when active, they are extremely difficult to follow. To make matters worse, the Black Hairstreak is often found in the company of both White-letter and Purple Hairstreaks and distinguishing these three species in flight is almost impossible.
A male feeding pictured below ...