Silver-studded blue  (Plebeius argus)

Protected by Schedule 5 of the Wildlife and Countryside Act, 1981, with respect to sale only (2).

Males are deep blue with a dark border and white fringe, and can be distinguished from other blue butterflies by the presence of a spur on the front legs (1). Females are brown, but both sexes possess metallic silver spots on the hindwings (3). The caterpillar grows to 1.3 centimetres in length, and is green in colour with a dark stripe along the back, and white stripes along the sides (4).

The silver-studded blue is widespread in temperate areas of Europe and Asia (3), but underwent a severe decline in Great Britain during the twentieth century (2). It has become extinct in most northern and central areas, parts of Wales and the North Downs. It is now largely restricted to heathland in Dorset and Hampshire (2), with a few populations in Wales, Suffolk, Norfolk Cornwall and Shropshire (5).

Found in lowland heathland, chalk grasslands, and some sand dunes. In all three habitats, the species needs short vegetation and ants of the genus Lasius (2). A supply of the main larval foodplants is also essential. These include a wide range of plants, the more common being heather, bell heather, cross-leaved heath and gorses on heathland, as well as common bird's foot trefoil, common rock-rose and horseshoe vetch on calcareous sites (3).

The adult flight period occurs between July and August on heathland and between June and mid-July on calcareous grasslands. There is a single brood a year; eggs are laid singly near the ground where they overwinter. The following spring the larvae hatch, soon after hatching they are closely tended by ants of the genus Lasius which are attracted by sugar-rich secretions produced by the caterpillar, and provide protection against predators. Pupation usually occurs in or near to ant nests, and the pupa continues to be protected by ants (5).

A number of factors contributed to the decline of this species, including widespread loss and fragmentation of heathland due to agricultural intensification, forestry and development. There has been a 60 percent loss of heathland in Britain, and remaining fragments have often become degraded due to a decline in traditional management techniques. The introduction of myxomatosis during the 1950s resulted in a huge decline in rabbit grazing and a loss of short vegetation. Chalk grassland habitats greatly declined as a result (6).

The remaining heathlands in Britain are the focus of huge conservation effort. A number of key silver-studded blue populations occur in nature reserves, Sites of Special Scientific Interest (SSSIs) and candidate Special Areas of Conservation. There have been a number of re-introductions of this species, and English Nature has produced a booklet on its conservation in lowland heathland (2). The silver-studded blue is a priority species under the UK Biodiversity Action Plan (UK BAP) (2).

For more information on the silver-studded blue see:

• Butterfly Conservation:
  www.butterfly-conservation.org/
• Butterfly Conservation's Species Action Plan:
  www.butterfly-conservation.org/downloads.asp?PageId=73
• Asher, J., Warren, M., Fox, R., Harding, P., Jeffcoate, G., and Jeffcoate, S. (2001) The Millennium Atlas of Butterflies in Britain and Ireland. Oxford University Press, Oxford.

Information authenticated by Butterfly Conservation:

http://www.butterfly-conservation.org/

• Calcareous: containing free calcium carbonate, chalky.
• Genus: a category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.
• Larvae: stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce
• Larval: of the stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
• Myxomatosis: a contagious viral disease in rabbits.
• Pupa: stage in an insect's development when huge changes occur, which reorganise the larval form into the adult form. In butterflies the pupa is also called a chrysalis.
• Re-introductions: attempts to establish a native species back into an area where it previously occurred.

1. Still, J. (1996) Collins Wild Guide: Butterflies and Moths of Britain and Europe.HarperCollins Publishers, London.
2. UKBAP Species Action Plan (March, 2002)
   http://www.ukbap.org.uk/UKPlans.aspx?ID=522
3. Asher, J., Warren, M., Fox, R., Harding, P., Jeffcoate, G. and Jeffcoate, S. (2001) The Millennium Atlas of Butterflies in Britain and Ireland.Oxford University Press, Oxford.
4. Carter, D.J. and Hargreaves, B. (1986) A Field Guide to Caterpillars of Butterflies and Moths in Britain and Europe.Collins, London.
5. Ravenscroft, N.O.M. and Warren, M.S. (1996) Species Action Plan: silver-studded blue, Plebejus argus.Butterfly Conservation, Wareham. Available at: http://www.butterfly-conservation.org/uploads/ssb_action_plan.pdf
6. Butterfly Conservation, Bulman, C. (2002) Pers. comm.