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Text and photographs protected by Copyright © Adrian Hoskins 2007, and must not be published in part or in whole elsewhere without prior written permission from the author.
Butterflies of Britain & Europe
 
Black Hairstreak
Satyrium pruni LINNAEUS, 1758
Family - LYCAENIDAE
subfamily - THECLINAE
Tribe - EUMAEINI
 
 introduction | habitats | lifecycle | adult behaviour
 
Black Hairstreak Satyrium pruni, male nectaring at bramble
 
Introduction
 
The Black Hairstreak is widespread across central and eastern Europe, but is absent from the Iberian peninsula, the Mediterranean coast, northern France, and most of Finland and Sweden. Throughout Europe it is considered to be a scarce and very localised species, although it's habitat requirements do not appear to be particularly specialised.
 
Beyond Europe it's range extends eastward through southern Siberia, Mongolia and Korea to Japan.
 
It is possible to confuse this species with the White-letter Hairstreak Satyrium w-album, which lacks the black spots on the underside, and in which the white median line forms a distinctive "W" shape. In continental Europe it can also be confused with the Blue-spot Hairstreak S. spini, the underside hindwing of which bears a perfectly straight white line, and a blue spot on the tornus.
 
Habitats
 
In Britain this species is a rarity, now confined to about 30 small woodland sites within a narrow strip of land running diagonally from Oxford to Peterborough.
 
At these sites the butterfly nearly always occurs as tiny populations, breeding on tall blackthorn bushes Prunus spinosa growing in sheltered and sunny situations. These are typically on the southern edge of a woodland, or in small glades, or along ride edges, but colonies also exist in hedgerows or in scrubby meadows close to woodland.
 
Blackthorn hedges that are trimmed are entirely unsuitable for this species. Almost all of the sites where it survives in Britain are specifically managed for the Black Hairstreak, by ensuring the retention of well established blackthorn hedgerows, and fencing them when necessary to prevent the bushes being grazed by cattle or deer.
 
Although the butterflies usually oviposit on long established bushes, good conservation also requires that new young bushes are encouraged, to ensure an uneven age structure of blackthorn. Bramble and privet bushes also appear to be significant elements in this species ecology, as they provide vital nectar sources for the adults.
 
Lifecycle
 
The butterflies are single-brooded, emerging in mid-June. The flight period is of very short duration, no more than 2-3 weeks, and individual butterflies appear to only live for about a week.
 
The brown disc-shaped eggs are laid singly on blackthorn twigs, usually on the sunlit side of the bush, at any height, and often close to forks in the twigs. They are laid in June or very early July.
 
The caterpillars are fully formed within the eggs by late July, but do not hatch until the following March when the flower buds appear.
 
When very young the caterpillars are dark brown, and rest on the unopened leaf buds. They feed at first on the flower buds, moving onto the leaf buds in April and May. As they develop they undergo several changes in colour and pattern. When fully grown in late May they are green, with pale diagonal stripes on each segment, and prominent pink-tipped ridges along the back. They feed diurnally, and rest fully exposed on the upper surface of the leaves.
 
In late May the pupa, which is black marked with white patches, and perfectly disguised as a small bird dropping, is formed attached by a silk girdle to a twig, or less commonly on the top of a blackthorn leaf.
 
Black Hairstreak Satyrium pruni, male at bramble
 
Adult behaviour

 

The adults emerge in the early morning, and shortly afterwards can sometimes be found settled on blackthorn twigs waiting for the wings to harden. Freshly emerged butterflies are brightly coloured and very beautiful, but within a day or two they become faded and worn, losing wing-scales and collecting superficial damage as they fly in and out amongst the thorns of blackthorn and bramble bushes.

 

On sunny mornings, and again in mid afternoon, the butterflies seek nectar, either at privet flowers, bramble, wayfaring tree or field rose. During the rest of the day they tend to remain stationary for long periods at the top of blackthorn bushes, where they feed on honey-dew ( aphid secretion ) which covers the upper surface of the leaves.

 

In late afternoon, when the changing position of the sun causes the bushes which they occupy to become shaded, they migrate across glades to seek the last remaining sunlit areas. They roost overnight on the upper surface of blackthorn leaves, amidst the tangle of growth within the bush.

 
                                                       
Almost every British and European species of butterfly is declining rapidly in numbers, due in most cases to loss or degradation of habitats.
 
You can help to reverse the decline by supporting conservation organisations which purchase and manage habitats as nature reserves, and which lobby government at local, national and international levels, often very successfully, to bring about changes in farming, forestry and urban development policies.
 
Please contact the conservation organisations for advice on how you can help protect British and European butterflies and their habitats. You may be able to offer practical help e.g. by monitoring butterfly populations or helping to manage nature reserves. Donations to these organisations enable them to employ ecologists and biologists. Even if you are unable to provide such help, merely having your name on the membership list can be a powerful tool for conservation organisations wishing to demonstrate the levels of support they have for their policies.

 

 
Text and photographs protected by Copyright © Adrian Hoskins 2007-2008, and must not be reproduced or published in part or in whole elsewhere in any form without written permission from Adrian Hoskins. Breach of copyright will be pursued by litigation.
 
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