Butterflies of Britain
Family - LYCAENIDAE
Lysandra coridon, male, Magdalen Hill
Down, Hampshire ©
A freshly emerged male
Chalkhill Blue is a particularly beautiful insect, with shimmering
silvery blue wings, and long hair-like scales adorning the body,
giving it a distinctly furry appearance. The wings are highly
reflective so the butterfly appears to be almost silver when seen in
The female can be confused with the female Adonis
Blue L. bellargus, but the upperside of
the latter has a deeper chocolate ground colour.
also has blue edging to the black sub-marginal spots on the
upperside, as compared to whitish edging in
The emergence of the 2nd brood of
bellargus overlaps slightly with
coridon during August, and both species
often share the same habitats.
Chalkhill Blue is distributed across much of Europe, but absent from
northern Britain, Ireland, northern Scandinavia, Portugal, southern
Spain and most of the Mediterranean islands. It's range extends into
western Asia as far as the Ural mountains.
Europe there are several species which closely resemble both sexes
of the Chalkhill Blue, and it is essential to consult a well
illustrated field guide to differentiate between them.
The butterfly breeds on
chalk and limestone hills, favouring south facing slopes where the
larval foodplant horseshoe vetch grows profusely amongst fine
grasses. The greatest numbers occur on sites that are grazed by
sheep, cattle or rabbits to produce a sward height of about 5 cms.
At the best sites the butterfly can occur in thousands, but it can
also survive at quite low densities at sites where grazing has been
abandoned and the grasses grow tall. At such sites they breed in
areas where the foodplant grows at the edge of paths, on patches of
scree, or abutting rabbit scrapes.
Colonies are very
localised, but not to the same degree as those of the Adonis Blue.
Thus coridon may be found spread widely
across it's sites, whereas bellargus is
usually restricted to tiny strips of land where the microhabitat is
Stray males are found
irregularly up to 8kms from the breeding sites, sometimes in quite
unsuitable habitats such as woodland clearings. Female strays are
almost unknown, and it is extremely unusual for the butterfly to
colonise areas away from their regular breeding sites.
species is single brooded, with a protracted emergence beginning in
early July and continuing into late August, with the last
individuals often seen well into September.
The reticulated, dome-shaped whitish eggs are
laid singly on stems of horseshoe vetch
Hippocrepis comosa or on nearby grass stems in August. During
the winter they are washed off by the rains and lie on the surface
until the spring. The larvae are fully formed within the eggs in the
autumn, but do not hatch until the following March or April.
plump green larva is marked with broken yellow lines along it's back
and sides. It rests under stones or chalk fragments during the
daytime, and feeds nocturnally. It can be found easily at dusk, when
large numbers of ants are in constant attendance. Ants will
sometimes grab hold of a larva to carry it closer to their nest,
milking it to obtain the sugary secretion exuded from it's honey
glands. In return for their reward, the ants protect the larva
against wasps and bugs.
pupa is a dirty greenish colour, and is formed on the surface of the
ground. Like the larva, it exudes secretions to attract ants, which
hide it by covering it with tiny fragments of earth, and guard it
against attacks by other insects. The gaps between the abdominal
segments of the pupa are armed with opposing sets of microscopic
serrations which can be rubbed together to create a rasping sound.
Just prior to emergence the butterfly within the pupa "sings" to
attract ants, which cluster around it, inadvertently protecting it
from predatory insects and arachnids. The ants never attack the
emerging butterfly, seemingly appeased either by the song, or
possibly by a pheromone.
Lysandra coridon, male, Stockbridge
Down, Hampshire ©
The butterfly, when it
emerges in July, has to break through the soil and find it's way to
a stem from which it can hang to dry it's wings. The adults often
emerge en masse,
and can sometimes be found basking in hundreds on low herbage early
in the mornings.
Favourite nectar sources
include marjoram, stemless thistle, carline thistle, knapweeds, wild
basil, self heal and thyme, although they will also visit bramble,
ragwort, yarrow and hemp agrimony. They also occasionally gather in
small groups on mammal dung.
In the French Alps I
have often seen males congregate in thousands to drink at patches of
mud or urine-soaked soil. Often there are several other species
present at these gatherings including Essex Skippers, Large Grizzled
Skippers and Heath Fritillaries, but each species polarises towards
its own kind, thus the Chalkhill Blues will cram very tightly
together in one spot, and the Essex Skippers etc will form their own
equally tightly packed groups just a few centimetres away.
Lysandra coridon, male, Old
Winchester Hill NNR, Hampshire ©
In southern Britain
one of the commonest predators of butterflies is the spider
Enoplognatha ovata, a member of the
family Theridiidae. This small species traps summer butterflies
which fly into the sticky strands of an untidy web which it spins on
grass-heads and wild flowers. I made a brief study of predation at
Magdalen Hill Down in Hampshire in mid-July 2009 and estimated that
a minimum of 5 percent of the population of Chalkhill Blues fell
victim to this spider.
coridon, male drying wings after emergence, Stockbridge
As dusk approaches the
butterflies migrate to the base of hills, where they roost
over-night on tall grasses, often with several males sharing a
single grass head, all resting in a head-downwards position.
Enoplognatha ovata, devouring
Chalkhill Blue Lysandra coridon ©
Lysandra coridon, female,
Stockbridge Down, Hampshire ©