Butterflies of Britain
Family - LYCAENIDAE
subfamily - THECLINAE
Tribe - EUMAEINI
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
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
Satyrium pruni, female
nectaring at bramble, Northants ©
this species is a rarity, now confined to about 30 small woodland
sites within a narrow strip of land running diagonally from Oxford
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.
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.
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.
antennae-dipping to "taste" nectar-source ©
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.
Satyrium pruni, female at
Satyrium pruni, female at
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, the red submarginal
band quickly fading to pale orange, and the rich golden brown ground
colour fading to greyish brown.
tend to sit motionless for very long periods at the top of blackthorn
bushes to intercept passing females. I have not observed any form of
pre-nuptial ritual, and it is likely that the butterflies copulate
almost immediately after meeting. Copulation usually occurs in late
at the top of blackthorn bushes, but the butterflies will often fly
short distances when copulated - I have for example seen photographs
of copulated pairs nectaring at bramble.
and sunny conditions females walk about on blackthorn twigs, usually
near the top of tall bushes, laying their eggs singly on or close to
forks in the twigs. After laying several eggs they take a period of
rest, and this is followed by a period of nectaring. The females
descend regularly to nectar at privet, bramble, dogwood, wayfaring
tree and field rose, but are very secretive and easy to overlook. They
tend to descend more frequently in warm muggy overcast conditions than
in full sunshine, and often spend several minutes sitting on a
particular bramble or privet flower. They also imbibe "honey-dew" -a
sugary secretion produced by aphids which coats the upper surface of
leaves, particularly blackthorn and ash.
female imbibing aphid secretion from the surface of nettle
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