Butterflies of
Britain & Europe
Green Hairstreak
Callophrys rubi
LINNAEUS, 1758
Family - LYCAENIDAE
subfamily -
THECLINAE
Tribe - EUMAEINI
Green Hairstreak
Callophrys rubi, male, Magdalen
Hill Down, Hampshire ©
Adrian Hoskins
Introduction
The genus
name of this delightful little butterfly - Callophrys
- is Greek for "beautiful eyebrows" and the species name
rubi refers to Rubus ( bramble ), one of the
caterpillars foodplants.
The
Green Hairstreak never displays it's brown upperside except when in flight. The
green colour of the underside ( like the blues and coppers of
other Lycaenids ) is produced by light refracting and reflecting
from a microscopic lattice within
translucent wing scales. The iridescent colouring
varies in hue according to the
directional qualities of the light and the angle of view. The
butterfly can thus appear to be metallic apple-green,
turquoise or emerald, when viewed from various angles.
Some individuals
known as form caecus have
plain undersides, but on others the wings are marked with a row of white
dots, often edged with reddish - these are called form
punctata.
The sexes are almost identical, but the male has a
small patch of scent scales
in the discal cell of the upperside forewing. This is also
visible in certain lighting conditions in the form of a little raised pad in the
cell on the underside.
Green
Hairstreak
Callophrys rubi, male, Magdalen Hill Down, Hampshire ©
Adrian Hoskins
Green Hairstreak
Callophrys rubi, female, Cerne
Abbas, Dorset ©
Adrian Hoskins
The
butterfly is widely distributed in Europe, all the way from the Mediterranean
islands to the far north of Norway and Sweden. It also occurs in Morocco and
Algeria, and in most of temperate Asia. There are many closely related
species elsewhere in the world, including the unfortunately named Sad Green
Hairstreak Cyanophrys
miserabilis of North
America, and several neotropical species.
In southern France, Spain, Portugal, Morocco and Algeria it
can be confused with Chapman's Green Hairstreak
Callophrys avis,
which occurs in dry scrubby areas and feeds as a larva on Arbutus.
They can be separated by examination of the eye borders, which in rubi
are white, but in avis
are reddish. The white dotted line on the underside is placed
centrally in avis,
but in the post-discal area in
rubi.
Habitats
The butterfly
occurs throughout most of the British Isles, but is quite localised, although
the range of habitats and larval foodplants used is very wide.
It is commonest on dry heathland, and on scrubby south-facing hillsides or warm sheltered valley bottoms,
particularly favouring habitats with hedgerows of hawthorn,
blackthorn,
bramble,
elder or gorse.
Most
colonies are small comprising no more than about 10-20 adults at peak season.
Many are even smaller, particularly at marginal habitats - e.g. along
railway cuttings, in woodland clearings or
at abandoned
chalk quarries.
At a few moorland sites in Cornwall and Cumbria however much larger populations
exist, numbering dozens or even hundreds of adults.
South facing chalk grassland slopes
like this are ideal Green Hairstreak habitats ©
Adrian Hoskins
Lifecycle
The butterflies emerge in early April in forward seasons, but
may be delayed until mid May in cool wet springs. They normally remain on the
wing until early June.
Females
roam widely over their habitat, laying their eggs singly on the
leaves or flower buds of the various foodplants,
including bird's foot trefoil
Lotus corniculatus,
common rockrose Helianthemum chamaecistus,
dogwood Cornus sanguinea,
buckthorn Rhamnus catharticus,
gorse Ulex europaeus,
and broom Cytisus scoparius. On moorlands and
heaths the main foodplant is bilberry Vaccinium myrtillus,
and in woodlands bramble Rubus fruticosus is
commonly used.
At Levin Down in Sussex, I watched a
particular female ovipositing over a half hour period on a hot sunny morning in
May 2006. She flew back and forth over a 20x50 metre
strip of hillside, carefully selecting each egg-laying
site, always choosing to lay on leaves of rockrose, despite the presence of bird's
foot trefoil and other known foodplants.
At Magdalen Hill Down, I watched another female behave in a
similar manner, depositing her pale green eggs meticulously onto the upper
surface of rock rose leaves, inserting them into the crevice formed where the base of the leaves emerges
from the stems.
At both sites the eggs were laid on plants growing on
ant-hills. This is probably because ant-hills tend to
be warmer than surrounding areas, but could also be
influenced by an association between the larva and
ants - many Lycaenid larvae are "milked" by ants, which drink a
sweet secretion
produced from a "honey gland" on the
back of the larva.
Green
Hairstreak
Callophrys rubi, male, Purbeck hills, Dorset ©
Adrian Hoskins
Like
other Lycaenid larvae, that of the Green Hairstreak is plump, like a woodlouse.
It is green, and marked with rows of yellow dots on the back and sides. The
larva feeds on the flower buds, flowers or tender young leaves of common
rockrose, gorse, bilberry, bird's
foot trefoil, dogwood, broom and various vetches. At
some sites the larvae feed on buckthorn berries, in which they make a hole
through which they extract the contents.
The
larva leaves the foodplant to pupate just under the surface of the ground, often
where there are stones or fallen leaves. The pupa
has the ability to produce a squeaking
noise - this was once thought to be a defence mechanism against ants and
beetles, but research on other Lycaenids that also share this behaviour suggest
that the pupa is actually "singing" to attract the attention of ants, which
carry it into their nests below the ground. The pupa secretes a sugary coating
which the ants drink, and in exchange the pupa gains protection from other
insects that would not dare enter the ants nest.
Adult behaviour
The
flight period is from
early
April until early June at the warmest sites; or from early May
until late June at cooler or northern sites.
Green Hairstreak
Callophrys rubi, Magdalen Hill Down, Hampshire ©
Adrian Hoskins
Males and females behave quite differently. Males
establish territories, typically perching on gorse flowers, or on the
foliage of hawthorn, blackthorn, elder,
privet
and various other bushes,
often at the bottom of hills.
On sunny mornings they use these perches as vantage points from
which they
dart
up to intercept
other
small insects, including bees, flies, and various butterfly
species, as well as other Green Hairstreaks.
When perching they regulate their body temperature by tilting
their wings - in cooler conditions they are angled to present the
maximum wing area to the sun but in hot conditions they are
angled edge
on to minimise heat absorption. This lateral-basking
technique
has the additional advantage that the wings cast no give-away
shadows, helping the already superbly camouflaged butterfly to
blend
even more perfectly against its background and avoid being
detected by predators.
Often several males will have overlapping territories, so male-male
encounters are frequent.
When
males
meet,
they engage in a
frenzied battle,
zipping about in tight circles,
each trying to outwit and outmanoeuvre the other with constant
changes of direction.
Each male changes his territory several times throughout the day
in response to the changing position of the sun which
causes each perch to become shaded at some stage. Thus the
butterflies frequently find themselves intruding into each other's
territories and often both males believe
they have "ownership" of a particular spot. At such
times their battles
can be protracted and intense. The pair will commonly spiral
rapidly to a height of about 4 metres, then break away. Invariably
however they soon meet again and continue the battle which may
last for several minutes. During this time they may chase each other up to 4
or 5 metres horizontally from
the point where the conflict began. Eventually the weaker male gives up
and leaves the vicinity, and the victor returns to his original perch.
I
have not observed courtship,
but
it is likely that the sexes copulate without any pre-nuptial
ritual. On several occasions I've
found copulated pairs settled on low herbage, but
they are difficult to
detect
due to the very effective cryptic colouration.
Females spend most of their time fluttering
inconspicuously
just above
the ground in search of egg-laying
sites, and are seen far less often than the males.
Both sexes
nectar at a wide range of spring flowers including bird's
foot trefoil,
horseshoe vetch, common vetch,
gorse,
common rock rose,
elder, holly, wayfaring tree, bluebells,
cowslip,
wood
forget-me-not,
dandelion, daisy
and hawthorn.
In
Dorset
I have observed Green Hairstreaks flying around elms and field
maples
at the bottom of chalk hills
in late afternoon, and settling for long periods on
ivy
foliage on
the higher branches
of small oaks, but have not been able to determine whether
both sexes indulge in this activity.
Green Hairstreak
Callophrys rubi, Cissbury Ring,
Sussex ©
Adrian Hoskins
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