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Text and photographs protected by Copyright © Adrian Hoskins 2007, and must not be published in part or in whole elsewhere without prior written permission from the author.
Butterflies of Britain & Europe
 
Large Blue
Maculinea arion LINNAEUS, 1758
Family - LYCAENIDAE
subfamily - POLYOMMATINAE
 
 introduction | habitats | lifecycle | adult behaviour
 
Large Blue Maculinea arion, female, south west England
 
Introduction
 
The 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, Buckinghamshire, south Devon, and at Barnwell Wold in Northamptonshire.
 
Many colonies were exterminated by collectors. By 1950 only 30 sites remained, and by 1970 only 3 or 4 colonies survived. The only remaining sites, in western Cornwall, were protected as nature reserves, but the populations dropped every year, largely due to under-grazing, which meant that the microclimate became too cool to support the ant Myrmica sabuleti, with which the butterfly has a symbiotic relationship.
 
The Large Blue became extinct in Britain in 1979.
 
During 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. At the time of writing ( June 2007 ) the Large Blue has become successfully re-established at several sites in Devon and Somerset, and it's future, at least in the short term seems assured.
 
In Europe there are 4 other Maculinea species with which arion can be confused. Males of arion sometimes have the black markings reduced or absent, leading to confusion with M. alcon. The pattern of black spots on the undersides is much heavier in arion than in other Maculinea species.
 
Large Blue Maculinea arion, female, south west England
 
Habitats
 
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 Gramat.
 
In Britain 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 for roosting.
 
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 20 per hectare where conditions are ideal.
 
Large Blue Maculinea arion, male, south west England
 
Lifecycle
 
The 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.
 
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. The plants chosen by the females usually have several open florets.
 
Large Blue Maculinea arion, female ovipositing on thyme, south west England
 
It is possible to find several eggs on the same flower-head, but these will have been laid by different females, or on return visits by a single female.
 
At one of the British sites, in June 2007 I observed 2 different females ovipositing on the flower buds of self-heal Prunella vulgaris ( see photo below ).  Unfortunately, although self-heal is closely related to thyme, larvae are unable to survive on this plant for more than a couple of days ( pers comm D. Simcox ), and always die.
 
Large Blue Maculinea arion, female ovipositing on self heal, south west England
 
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 and final instar it loses interest in feeding, becomes restless, and eventually loses 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, which stimulates the larva to secrete a honey-like fluid from a "Newcomer's gland" on it's back. After feeding on the fluid, the ant wanders off, but returns periodically to further "milk" the larva.
 
After several milking sessions the larva becomes immobile, hunching it's back, and allows the ant to seize it and carry it into the brood chamber of the ant nest. At this stage the larva becomes carnivorous, feeding for the next 6 weeks on tiny ant grubs.
 
In early September the larva enters hibernation, remaining quiescent until the following April, when it resumes feeding on the ant grubs. During this carnivorous stage the larva is tolerated by the adult ants in exchange for providing them with a regular supply of "honey" from it's dorsal gland.
 
It is likely that the ants are further appeased by pheromones emitted by the larva, and that these pheromones are also emitted by the pupa, which lies within the ant nest for 3 weeks, unprotected by any form of cocoon.
 
The adult butterfly emerges within the nest, 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.
 
Large Blue Maculinea arion, female, south west England
 
Adult behaviour

 

The adults fly rapidly over short distances, settling periodically to nectar or to rest with closed wings, on plant stems. 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. They do however appear to have excellent powers of dispersal, and are able to extend their range locally by using road embankments and other corridors.

 

In overcast but warm conditions they bask with wings held half open, on bushes or amongst grasses. Nectar sources favoured in Europe include marjoram and thistles, but in Britain I have only observed them nectaring at thyme, red clover, and white clover.

 

I have not observed the courtship ritual, if any exists, but have found copulated pairs settled on thistle stems. If disturbed, mated pairs are very reluctant to fly.

 

The butterflies roost overnight under bushes, or amongst tall grasses, usually where these occur in sheltered depressions.

 

Large Blue Maculinea arion, female at roost, south west England

 
                                                       
Almost every British and European species of butterfly is declining rapidly in numbers, due in most cases to loss or degradation of habitats.
 
You can help to reverse the decline by supporting conservation organisations which purchase and manage habitats as nature reserves, and which lobby government at local, national and international levels, often very successfully, to bring about changes in farming, forestry and urban development policies.
 
Please contact the conservation organisations for advice on how you can help protect British and European butterflies and their habitats. You may be able to offer practical help e.g. by monitoring butterfly populations or helping to manage nature reserves. Donations to these organisations enable them to employ ecologists and biologists. Even if you are unable to provide such help, merely having your name on the membership list can be a powerful tool for conservation organisations wishing to demonstrate the levels of support they have for their policies.

 

 
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