The black hairstreak is a Species of Conservation Concern in Britain. It has always lived in a very small range in the former Royal forests in the east Midlands, but this range has declined because of changes in woodland management. The black hairstreak is now restricted to a belt of woodlands between Oxford and Peterborough.
Black hairstreak (Satyrium pruni)
The black hairstreak has fairly specific habitat requirements. It prefers dense, mature stands of Blackthorn, growing in sheltered positions alongside rides and clearings in woods and woodland edges. Sometimes they live in more exposed conditions, such as in hedgerows or gaps in the canopy of mature woodland. Its restricted range was encouraged by the long rotation (20-40 years) coppicing in the former Royal forests that allowed mature stands of Blackthorn to develop.
The black hairstreak is a solitary butterfly. Colonies tend to breed year after year in the same small area of habitat. Individual eggs are laid on mature blackthorn bushes in the autumn and develop over the winter.
Caterpillars hatch in the spring. Adult butterflies fly throughout June and July. They can be difficult to spot because they spend much of their time up in the tree canopy.
Caterpillars feed on blackthorn and occasionally wild plum. Adult butterflies feed on the honeydew produced by aphids of field maple and ash trees.
Mature blackthorn habitat has been isolated and fragmented through replanting with conifers and by loss of hedgerows and woodland to agriculture. Pressure from deer browsing also means that new stands of blackthorn are not being allowed to regenerate naturally.
The underside of the wing has a distinctive row of black spots in the outer orange margin, and a pattern of white in the shape of a 'W'. It is easy to confuse this species with the white-letter hairstreak and the purple hairstreak.
How we manage our woods
Sympathetic management by the Forestry Commission, working in partnership with Butterfly Conservation, has stabilised numbers in many black hairstreak colonies. Conservation depends on the protection of existing stands of mature blackthorn. Replanting blackthorn and allowing natural regenerating will create new habitat.