Butterflies of Britain
Family - LYCAENIDAE
Maculinea arion, female, Collard Hill,
Large Blue is widely distributed across Europe, but absent from
southern Spain, Portugal, northern Scandinavia, and most
Mediterranean islands. It's range also includes Turkey, Russia,
western Siberia, Mongolia, temperate China and Japan.
Since the discovery of the first British colony in 1795, the
butterfly has always been considered a rarity. In the 19th century,
collectors searched far and wide, successfully locating colonies at
sites including the cliffs of Dover, Marlborough Downs, Winchester,
Somerset, the Cotswold hills, south Devon, Buckinghamshire, and at
Barnwell Wold in Northamptonshire.
Butterfly collecting was an obsession among the
middle classes during the Victorian period, and the Large Blue was
regarded as a major trophy which could be sold for substantial
profit. As a direct result most colonies were exterminated by
collectors. By 1950 only 30 sites remained. The spread of
myxomatosis then caused the collapse of rabbit populations, and as a
consequence the sites quickly became under-grazed, and the
microclimate became too cool to support the ant
Myrmica sabuleti, with which the
butterfly has a symbiotic relationship. By 1970 only 3 or 4 colonies
survived, all on nature reserves. Populations however continued to
decline dramatically, and the
Large Blue became extinct in Britain in 1979.
the 1980's, following extensive research into the butterfly's
ecology by Dr Jeremy Thomas, plans were laid to reintroduce the
butterfly using livestock imported from Sweden. These
reintroductions, mostly on private nature reserves, met with varying
degrees of success.
the time of writing (2012) the Large Blue has become successfully
re-established at several sites in Devon and Somerset, and it's
future in Britain, at least in the short term seems assured.
Large Blue ovipositing ( note egg already laid on lower right of
thyme flower ), "site H", Somerset
In Europe the
butterfly can be found in a wide variety of habitats including
coastal cliffs, limestone gorges, stony plateaux, and alpine
pastures. In France for example I have found colonies as high as
2000m in Vanoise National Park, at 1500m on Mont Dore in the Massif
Central, and at roadside verges and woodland glades at Causse de
the butterfly is confined to a small number of dry calcareous
grassland hills in Devon and Somerset, where thyme grows in
profusion, and where the microclimate is warm enough to allow the
ant Myrmica sabuleti to flourish.
Maintaining these conditions normally requires a program of cattle
and / or sheep grazing. The butterfly also benefits from the
presence of a limited amount of scrub, typically gorse or hawthorn,
and thrives best where sheltered areas of long grass are available
Colonies everywhere tend to be small, typically less than 20 adults,
but I know of well managed sites where up to 70 butterflies can be
seen in a day, distributed over an area of several hectares.
Population densities normally vary between 2 - 10 butterflies per
hectare, but can be as high as 50 per hectare where conditions are
Maculinea arion, male, "site H",
butterfly emerges in June, or sometimes in early July. The entire
flight period in Britain spans about 40 days, with individual
butterflies living for up to 2 weeks, although the average lifespan
is only about 5 days.
The pale bluish-white eggs are laid singly on the
flower buds of various plants in the family Labiatae - favouring
marjoram in lowland areas of France, but usually selecting thyme
Thymus pulegioides in the Alps and in
Britain. Females usually choose plants which have several open
It is possible to find several eggs on the same
flowerhead, but these will have been laid by different females, or
on return visits by a single female.
Maculinea arion, female, "site H",
At one of the British sites, in June 2007 I
observed 2 different females ovipositing on the flowerbuds of
self-heal Prunella vulgaris. This plant
is closely related to thyme but unfortunately the larvae are unable
to survive on it for more than a few days and invariably die.
Maculinea arion, female ovipositing on
self heal, "site H", Somerset ©
The caterpillars hatch after 7-8 days, and begin
feeding on the flower sepals, on which they are well camouflaged.
They eat holes in the sepals to enable them to reach and feed upon
the developing seeds. Each larva needs to eat every seed on the
flower-head if it is to survive to the fourth instar, and will eat
attack any competing caterpillar that it encounters, and eat it to
ensure that it has sole access to all the seeds on the plant.
Upon reaching the fourth
( final ) instar it
loses interest in feeding, becomes restless, and eventually releases
it's grip on the foodplant and falls to the ground. It wanders about
until it is located by an ant of the species
Myrmica sabuleti or M. scabrinodis.
The ant then begins to caress the larva with it's antennae. This
stimulates the larva to secrete a honey-like fluid from the
"Newcomer's gland" on it's back. After drinking the honey the ant
wanders off, but returns later with other ants to further "milk" the
After several milking sessions the larva becomes immobile, hunching
it's back, and allows an ant to seize it and carry it into the brood
chamber of the ant nest. Once settled in its new home the larva
becomes carnivorous, feeding on tiny ant grubs.
Only the largest
ant nests produce the 1500 or so grubs that are necessary for the
Large Blue larva to complete its growth.
larva is tolerated and protected by the adult ants in exchange for
providing them with a regular supply of "honey" from it's dorsal
gland. It is also likely that the larva emits pheromones which
appease the ants and assure its safety.
early September the Large Blue larva enters hibernation, remaining
quiescent until the following April, when it resumes feeding on the
ant grubs. In May pupation takes place within the ants brood
chamber, where the pupa is unprotected by any form of cocoon. Like
the larva, it exudes "honey", and is constantly attended by the
Three weeks later the adult butterfly emerges within the nest, but
immediately before emergence the pupa produces a rasping "song"
which stimulates nearby ants into a frenzy. The butterfly then
breaks out of the pupa, and with it's wings still tiny and limp,
crawls along the ant tunnels until it reaches the surface, where it
climbs a stem and hangs to expand and dry it's wings. Throughout
this time the highly vulnerable butterfly is constantly surrounded
by the ants. They make no attempt to attack it - their presence in
fact acts as a very strong deterrent to any other creature that may
be considering the Large Blue as it's next meal. The butterfly
almost certainly therefore is able to appease the ants, by releasing
a chemical that either warns that it is distasteful, or mimics the
smell of something that the ants find repellent or dangerous.
Research on the
closely related European species Maculinea
rebeli has shown that its larvae are parasitised by the
wasp Ichneumon eumerus. The wasp
enters the ant brood chamber where it releases a chemical which
causes the ants to fight among themselves. The larva is thereby
rendered defenceless and vulnerable to attack by the wasp.
The adults fly rapidly
over short distances, settling periodically to nectar or to rest with
closed wings, on plant stems. They are deceptively strong flyers, and
if disturbed they will fly up to 100 metres before settling. I have on
several occasions observed Large Blues fly over tall hedges, or
attempt to cross open fields, but invariably after a few seconds of
investigation the butterflies return to their habitat. In June 2009, I
closely followed a particular female at "site H" in Somerset and noted
that it's "home range" extended a distance of almost a kilometre from
one end of the site to the other, and that it oviposited on plants
right across the site. This site was in fact colonised naturally from
a nearby introduced colony, and it is apparent hat the butterfly has
excellent powers of dispersal provided that areas of its habitat are
In overcast but warm
conditions they bask with wings held half open, on bushes or amongst
grasses. On sunny mornings both sexes fly along the bottom of slopes,
where the very brief courtship flight takes place. The female then
settles on a bush or among grasses, followed closely by the male, who
crawls alongside her, and then curves his abdomen to make contact. In
England and France I have found copulated pairs sitting half way up
thistle stems, low down on grass blades, and sitting on bare ground or
behaviour takes place in the afternoon, when the butterflies settle
for a moment here and there to feed at the flowers of marjoram,
thistles, thyme, red clover and white clover.
butterflies roost overnight under bushes, or amongst tall grasses,
usually where these occur in sheltered depressions.
Maculinea arion, "site H", Somerset ©