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Butterfly Conservation- Glasgow & South West Scotland Branch


Common Blue (Polyommatus icarus)

Description

The Common Blue is a beautiful little butterfly (wingspan 29-36 mm) found widely distributed across South West Scotland. The male is often slightly larger than the female and has white-fringed upperwings that vary from brilliant blue to violet blue. The female upperwings are usually brown with a touch of blue near the wing base and orange spots around the edges, but in South West Scotland females tend to have predominantly blue wings, particularly those of the Marsicolore race. The underwings of both sexes are brownish with black spots circled by white and orange spots near the outer edge. Their charming eyes are typical of lycaenids with a white ring around them. Until recently this was the only blue-coloured butterfly likely to be seen in our area, but the Holly Blue (Celastrina argiolus) is currently expanding northwards and may potentially cause confusion if seen from a distance.

Credit: Neil Gregory
Credit: Jim Black
Credit: Scott Shanks

Life Cycle

After emerging, the azure males set about defending territories and finding mates, often chasing other species that come to nectar at Ďtheirí flowers. Females tend to be less conspicuous, resting or basking in the sun to conserve energy between nectaring and searching for suitable sites to lay their eggs. In South West Scotland a single brood is produced each year, although further South two or even three broods can be produced during a good year. The white disc-like eggs are laid singly on tender new leaves of birdís-foot trefoil (Lotus corniculatus) the main larval food plant, but greater birdís-foot trefoil (Lotus pendunculatus), black medick (Medicago lupulina) and white clover (Trifoilium repens) may also be used. After hatching, the green grub-like larvae feed until half grown (~6mm) before going into hibernation on the lower stems of the food plant or in the leaf litter. In the Spring the larvae continue feeding until their final instar (~13 mm) when they become attractive to ants. The green pupae also produce sugary secretions known to be attractive to ant species.

Flight Times

In South West Scotland adults can be found on the wing from June to September in one protracted brood, with numbers peaking during July. Further North adults tend to emerge later, flying from late July to September.

Habitat & Distribution in SW Scotland

Distribution map 2010

The Common Blue is widely distributed through out South West Scotland. It can be found in a wide range of grassy places where its larval food plants grow such as coastal dunes and undercliffs, road verges and disturbed waste ground. It favours short flower-rich grassland, where the soil has poor fertility, and frequent bare patches where the butterfly can bask in the sun. Pockets of tall grass or reeds are used as roost sites where the adults rest head-down in the evenings. It is normally associated with dry sites, but wetter areas may be colonised if greater birdís-foot trefoil is present. Colonies tend to be relatively small, but butterfly numbers can respond quickly to increased abundance of its larval food plant at disturbed or brownfield sites.

At present the Common Blue has a stable distribution in South West Scotland and is currently not a species of conservation concern, however some strong colonies at brownfield sites may have been lost to expanding housing developments. The status of this species provides a strong indication of the state of biodiversity in the wider countryside

References

  • Futter, K., Sutcliffe, R., Welham, D., Welham, A., Rostron, A., MacKay, J., Gregory, N., McCleary, J., Tait, T., Black, J. & Kirkland, P. 2006. Butterflies of South West Scotland. Argyll Publishing. (see Atlas page)
  • Asher, J., Warren, M, Fox, R., Harding, P., Jeffcoate, G., Jeffcoate, S. 2001. The Millennium Atlas of Butterflies in Britain & Ireland. Oxford University Press.
  • Fox, R., Asher, J., Brereton, T., Roy, D., Warren, M. 2006. The State of Butterflies in Britain and Ireland. Pisces Publications.
  • Tomlinson, D. & Still, R. 2002. Britainís Butterflies. WILDGuides

Written by Scott Shanks


 
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