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Text and photographs protected by Copyright © Adrian Hoskins 2007, and must not be published in part or in whole elsewhere without prior written permission from the author.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
 
Common Blue
Polyommatus icarus ROTTEMBURG, 1775
Family - LYCAENIDAE
subfamily - POLYOMMATINAE
 
 introduction | habitats | lifecycle | adult behaviour
 
Common Blue Polyommatus icarus, male, Ballard Down, Dorset, England
 
Common Blue Polyommatus icarus, female ( 2nd brood ), Ballard Down, Dorset, England
 
Introduction
 

Despite it's name, the Common Blue can no longer be considered a common butterfly. It certainly remains the most widespread "blue" in Britain, but many colonies in marginal habitats such as woodland rides and farmland have declined or been lost. The butterfly can still be found in good numbers on calcareous grasslands, but the colonies rarely comprise of more than a few dozen individuals.

 

Common Blue Polyommatus icarus, male, Ballard Down, Dorset, England

 

Males are very consistent in appearance, the uppersides being violet-blue with plain white fringes ( unlike the sky-blue males of Adonis Blue which have chequered fringes ). Females vary considerably - some are heavily dusted in violet-blue scales, often with smudges of greyish, while others are almost devoid of blue and strongly resemble the Brown Argus Aricia agestis.

 

Common Blue Polyommatus icarus, female, Ballard Down, Dorset, England

 

The undersides of both sexes of Common Blue are marked with a pattern of white-ringed black spots and orange crescents. Sometimes aberrant forms can be found in which the black spots are elongated into a series of short bars. Other rare forms occur in which the spots may be reduced in size, or entirely absent. In all forms the male has a greyish ground colour with bluish scales around the base of the wings. Females have greenish scales at the wing bases, and a pale brown ground colour.

 

All butterflies in the subfamily Polyommatinae have undersides patterned with black spots, including several European species in the genera Plebejus, Polyommatus and Agrodiaetus. Several of these can be confused with the Common Blue. The number and arrangement of the spots is different in each species however, so close examination of the markings and the use of a well illustrated field guide will enable the various species to be differentiated.

 

The Common Blue is found throughout Europe, from the extreme north of Scandinavia to the smallest islands of the Mediterranean. Beyond Europe, it's range extends from the Middle East across temperate Asia to northern China. It also occurs in northern Africa and the Canary Islands.

 

Common Blue Polyommatus icarus, copulated pair ( male on left ), Martin Down NNR, Hampshire
 
Habitats
 
The butterfly is found throughout England, Scotland and Wales at sites where bird's foot trefoil grows in profusion. It is most abundant on chalk or limestone grassland but also occurs in lesser numbers in woodland clearings, meadows, heathlands, sand dunes, along railway cuttings, riverbanks and undercliffs. Numbers are usually highest on south facing hillsides.
 
In Europe it also occurs on mountains at altitudes up to 2700m, arid scrubland, glades in pinewoods, marshland and many other habitats.
 
Common Blue Polyommatus icarus, male, Ballard Down, Dorset
 
Lifecycle
 
In Britain there are 2 generations per year. The first brood emerges in mid May and flies until mid June. The second brood emerges in late July or early August and remains on the wing until mid September.
 
The circular, flattened white eggs are laid on the underside of terminal leaves of bird's foot trefoil Lotus corniculatus, greater bird's foot trefoil L. uliginosus, black medick Medicago lupulina, restharrow Ononis repens and other leguminous herbs.
 
The larvae are pale green in colour, and feed diurnally. Like most Lycaenid species they are often attended by ants, which milk the larvae for sugary secretions. The larvae in exchange are protected by the ants from predatory insects. The relationship is not symbiotic however - captive larvae prevented from making contact with ants survive well and produce healthy adult butterflies.
 
Larvae of the 1st brood feed up quickly to produce butterflies in late summer. Those of the 2nd brood hibernate when quite small, reawakening in March to resume feeding.
 
The chrysalis is pale green, with the wing cases tinged with buff. The shed larval skin remains attached to the tip of the abdomen. Ants are attracted to the newly formed chrysalis ( probably by pheromones ) and quickly cover it with particles of soil and leaf litter. The pupal stage lasts for about 2 weeks.
 
Common Blue Polyommatus icarus, male in typical basking posture, Ballard Down, Dorset
 
Adult behaviour
 
In weak sunlit conditions males often bask on low herbage, with wings held half open. In overcast but warm conditions they sometimes bask with wings fully outspread.
 
When the weather is warm and sunny they fly actively from flower to flower, nectaring in spring at plants including bird's foot trefoil, buttercup, daisy, black medick, hop trefoil, hoary plantain, speedwell, heath milkwort, field forget-me-not and comfrey.
 
Summer brood butterflies particularly favour fleabane, ox-eye daisy and marjoram.
 
When males encounter females they attempt to copulate immediately without any form of courtship ritual. Mated pairs often sit in prominent positions on grass-heads or on the flowerheads of plantain or salad burnet.
 
The females are seen less often, being less conspicuously coloured, and more sedentary in behaviour.
 
Common Blue Polyommatus icarus, male nectaring at plantain
 
Both sexes roost overnight on grass heads, facing head-downwards, often in groups of up to 5 individuals. Roosting at the top of the grasses is probably an effective survival strategy, keeping them out of reach of mice and other nocturnal predators.
 
                                                       
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.

 

 
Text and photographs protected by Copyright © Adrian Hoskins 2007-2008, and must not be reproduced or published in part or in whole elsewhere in any form without written permission from Adrian Hoskins. Breach of copyright will be pursued by litigation.
 
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