Butterflies of
Britain & Europe
Holly Blue
Celastrina argiolus
LINNAEUS, 1758
Family - LYCAENIDAE
subfamily -
POLYOMMATINAE
introduction
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habitats |
lifecycle |
adult behaviour
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Holly Blue
Celastrina argiolus, 1st brood male, Purbeck Hills,
Dorset |
Introduction
This
is a very widely distributed species, found throughout the temperate regions of
Europe, in North America from Alaska to Panama, across temperate Asia to Japan,
and in Africa north of the Sahara. Another very similar species Celastrina lavendularis
is found in the temperate highland areas of India and south-east Asia, and 2
further Celastrina species are found in Indonesia and Papua New Guinea.
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Holly Blue
Celastrina argiolus, 2nd brood female,
Broughton Down, Hampshire |
The
distinctive black wing-tips of the female ensure that it can't be mistaken for
any other European species, but the male can be confused in flight with the
Common Blue, which also sometimes flies in scrubby habitats. The underside of the
Holly Blue however is quite different, being a highly reflective silvery blue,
with tiny black dots and dashes.
Like most British butterflies, the
Holly Blue has had several earlier vernacular names which have since fallen into
disuse. The male of this species was once called the Wood Blue or Azure Blue,
while the female, which early entomologists thought was a different species, was
known by the very apt and descriptive name "Blue Speckt Butterfly with Black
Tips".
Holly Blue
Celastrina argiolus, 1st
brood female, Herts
( photo © Emily Halsey )
Habitats
In Britain the Holly Blue is
largely confined to England and Wales, although there are very sporadic records
from Scotland and Ireland.
The butterfly is adapted to utilise a wide range of
common larval foodplants including non-native ornamental species. Consequently
it can be found in
gardens and city parks as well as at woodlands, heaths, old quarries and railway cuttings.
Most
habitats tend to be sheltered, but I have on several occasions seen pristine
Holly Blues flying rapidly across open heathland e.g. in the New Forest ( Hampshire )
and Wareham Heath ( Dorset ). From the latter observation it is apparent that
the butterflies are highly mobile, and able to colonise new sites quickly. This
mobility and the polyphagous nature of the larvae, ensures that the species is
widely and evenly distributed within its range.
Lifecycle
Throughout it's range, the species
is double brooded. In Britain, butterflies of the first brood
begin emerging in March at the warmest sites, but April or May
is more typical. The second brood flies from July until mid
August. There is occasionally a partial third brood, emerging in
September and October.
Older literature suggests that the
butterfly oviposits on holly in the spring, and on ivy in the
summer, but both broods in fact use a very much wider range of larval
foodplants.
The eggs of the first brood are
laid
singly on flower
buds of holly
Ilex aquifolium, dogwood
Cornus sanguinea, gorse
Ulex europaeus, or buckthorn
Rhamnus catharticus. The
second brood oviposit on
flower buds of ivy
Hedera helix, privet
Ligustrum vulgare, heather
Calluna vulgaris, alder buckthorn
Frangula alnus, bramble
Rubus fruticosus, rowan
Sorbus aucuparia and
various other bushes and shrubs including cultivated snowberry and
Pyracantha.
The eggs are nearly always laid on bushes growing in warm sunny
and sheltered situations. They hatch after about a week.
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female ovipositing
on dogwood flowers, Stockbridge Down |
The green slug-like caterpillars feed
nocturnally on the
flower buds, developing seeds and berries of the various
foodplants, and rarely on the young tender leaves. They
habitually sit on the skin of a berry, with their head buried
inside it. The caterpillar is easy to find, either by searching
directly, or by looking for half eaten berries in which the
caterpillar has left a distinctive circular hole.
As well as the plain green form of the caterpillar, there are
also forms with prominent whitish and purplish markings. In common
with most Lycaenids, the larvae are attended by various species of
ants, which obtain sugary secretions from a gland on the
caterpillar.
The larvae are parasitised by a
host-specific ichneumon wasp
Listrodomus nycthemerus,
which has a very pronounced
effect on Holly Blue abundance. In certain years, when climatic
conditions favour the parasitoid, the butterflies can be
extremely scarce. However when mild winters are followed by hot summers the
wasps emerge out of synchrony with the caterpillars,
and consequently in such years the butterflies are far more
common.
The dark brown pupae are
virtually impossible to find in the wild, but in captivity they
are attached by a silken girdle to a twig or dead leaf. In
nature they are probably formed in
crevices in tree bark, or amongst leaf litter on the forest
floor. The species over-winters in the pupal stage.
Adult behaviour
Most of the "blues" found in Britain and Europe form breeding colonies of
dozens, hundreds or even thousands. They generally inhabit open
grassy habitats and fly close to the ground. In contrast the Holly Blue is nearly always
encountered singly, and found in the vicinity of bushes, shrubs
and the lower branches of trees. It is also very unusual in that
it is more commonly encountered in gardens and parks than in the
wild countryside.
Holy Blues commonly feed on the aphid secretions ( honey dew )
which coats the upper surface of ash and oak leaves, but also
sometimes
settle on the ground to feed at bird droppings or imbibe moisture
from damp paths. Additionally, in spring they nectar at hawthorn,
daisies and wood spurge. The second brood nectars on a wider range
of plants including bramble, hemp agrimony, fleabane, bell
heather, cross-leaved heath, hogweed, cow wheat and burdock.
When feeding they always keep their wings closed, but in the hazy
sunshine of early evening they often settle on bushes to bask,
holding their wings partly open.
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