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Text and photographs protected by Copyright © Adrian Hoskins 2007, and must not be published in part or in whole elsewhere without prior written permission from the author.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
 
Holly Blue
Celastrina argiolus LINNAEUS, 1758
Family - LYCAENIDAE
subfamily - POLYOMMATINAE
 
 introduction | habitats | lifecycle | adult behaviour
 

Holly Blue Celastrina argiolus, 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.
 
Holly Blue Celastrina argiolus, female, Blean Woods, Kent, England
 
The distinctive black wing-tips of the female ensure that it cannot 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.
 
Habitats
 
In Britain the species is largely confined to England and Wales, although there are occasional records from Scotland and Ireland.
 
The butterfly is adapted to utilise a wide range of common larval foodplants, including non-native ornamental species, so consequently 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 across open heathland e.g. in the New Forest ( Hampshire ) and Wareham Heath ( Dorset ).
 
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 much wider range of larval foodplants.
 
The eggs of the first brood are laid singly on the flower buds of holly Ilex aquifolium, gorse Ulex europaeus, buckthorn Rhamnus catharticus, or dogwood Cornus sanguinea. The second brood lay their eggs on the flower buds of ivy Hedera helix, privet Ligustrum vulgare, heather Calluna vulgaris, bramble Rubus fruticosus, rowan Sorbus aucuparia, alder buckthorn Frangula alnus, and various other bushes and shrubs including cultivated species such as snowberry and Pyracantha. The eggs hatch after about a week.
 
Holly Blue Celastrina argiolus, 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. In common with most Lycaenids, they 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. Hot summers and mild winters seem to cause the parasitoids to emerge out of synchrony with the caterpillars, and consequently in such years the butterflies are far more common.
 
The dark brown pupae are formed in crevices in tree bark, or amongst leaf litter on the forest floor. The species over-winters in the pupal stage.
 
Holly Blue Celastrina argiolus, male at bramble, Stockbridge Down, Hampshire
 
Adult behaviour

 

Most "blues" found in Britain and Europe form breeding colonies of dozens, hundreds or even thousands, and generally inhabit open grassy habitats. The Holly Blue however 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.

 

When at rest the butterflies normally sit on the foliage of bushes, but sometimes they settle on the ground, feeding at bird droppings or imbibing moisture from damp paths. They nectar in spring at hawthorn, daisies and wood spurge. The second brood nectars on a wider range of plants including hemp agrimony, fleabane, hogweed, cross-leaved heath, bell heather, bramble, cow wheat and burdock.

 
                                                       
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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