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Butterfly Conservation- Glasgow & South West Scotland Branch


Northern Brown Argus (Aricia artaxerxes)

Description

The Northern Brown Argus is a striking little butterfly with dark slate-brown wings (26-35 mm wingspan) edged by orange lunuals (crescent shapes), a white fringe and either a white or black spot in the middle of the forewing upper surface. There are two distinct subspecies of the butterfly in Britain: In the North of England the salmacis race has a black spot on the upperside of the forewing, while the Scottish artaxerxes subspecies has a characteristic white spot. Both sexes of the Northern Brown Argus are similar in appearance, with the female having a greater number of lunuals edging the upper forewing. In south West Scotland, the Pallidior colour form can also be found which has pale yellow lunuals instead of the usual orange. The underside of their wings are pale gray-brown with many white spots and a few black dots, similar to those of the common blue. In flight they can appear silvery brown as they flit from flower to flower.

Credit: Scott Shanks
Credit: Scott Shanks
Credit: Anon

Life Cycle

After emerging in late May/early June, the adults set about forming territories and finding mates with much nectaring and basking in the sun too. The disc-shaped pale blue-green eggs are laid on the upper-surface of the leaves of common rock-rose (Helianthemum nummularium), the main larval food plant. It is thought that in South West Scotland, they may also use bloody cranesbill (Geranium sanguineum) or other members of the geranium family as larval food plants. After hatching, the small green woodlouse-like caterpillars move to the underside of the leaves to feed. Only one generation is produced per year, and after feeding until October the caterpillar goes down into the leaf litter to hibernate. In April the caterpillar resumes feeding and basking in the Sun once more. After hibernation larvae have been observed being attended by ants that are attracted by pheromone-producing organs on the caterpillar abdomen. When fully grown (12 mm) the caterpillar forms a green-brown pupa either on a silken mat on the ground or attached to low vegetation by silk threads.

Flight Times

In South West Scotland adults can be found on the wing from late May to mid-August, with a peak in numbers from mid June to the end of July. In the north of Scotland it emerges later, and can be found right up to September. The adults within a colony tend to be quite sedentary, moving only 20-30 m over the course of a few days, but occasional adventurous individuals may wander as far as 150 m looking for mates or a suitable site for laying eggs.

Habitat & Distribution in SW Scotland

The Northern Brown Argus is found locally along the coast of Dumfries and Galloway, and South Ayrshire. There are also a few inland sites where it may be found including the excellent Butterfly Conservation reserve at Mabie Forest near Dumfries (NX950710). Favoured habitat is generally South-facing well drained, unimproved grassland on limestone-rich basic soils with low levels of grazing. These conditions support a rich flora including the common rock-rose the main larval food plant, as well as bloody cranesbill, thyme and birds-foot trefoil. Interestingly, colonies of Northern Brown Argus can be found at locations along the Ayrshire coast where no rock-rose grows. It appears that at such sites the butterfly uses bloody cranesbill or other members of the geranium family as larval food plants.

Distribution map 2010

Northern Brown Argus colonies are declining at many sites due to overgrazing, habitat fragmentation or change in management. Recent research has shown that colonies respond well to positive habitat management techniques such as changing from heavy grazing by sheep to low intensity winter or spring grazing.

In England where the Northern Brown Argus can be found together with the Brown Argus (Aricia agestis), hybridisation between the two species has been known to occur.

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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