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Butterfly Conservation- Glasgow & South West Scotland Branch

Scotch Argus (Erebia aethiops)

Description

The Scotch Argus when newly emerged is a stunningly beautiful butterfly which has dark brown or almost black velvety wings with orange bands on the upperwings containing conspicuous eye spots. The sub species which occurs in Scotland is called caledonia which has a narrowing of the orange band on the upper forewing between the top two and bottom eyespots. During the latter half of the flight period, most individuals do have a worn tatty appearance in contrast to the stunning newly emerged individuals.

The underside of both the male and female are variable: the female has the lower hindwing as either pale-yellow-brown or dark brown with a grey-violet band; the male hindwings can be a striking dark chocolate brown with a broad grey-violet band or paler brown.

Credit: Anon
Credit: Jim Asher
Credit: Jim Black

Life Cycle

The pale yellow eggs are laid singly on vegetation close to the ground. The foodplant is Purple Moor-grass although other grasses such as Tufted Hair-grass, Wavy Hair-grass, Sheep's Fescue & Common Bent may also be eaten.

The caterpillars rest by day and only emerge at dusk to feed on the tips of grass blades. The caterpillars hibernate overwinter when still quite small within grass tussocks and resume their nocturnal feeding in early spring until they are ready to pupate in late June or early July.

Flight Times

The Scotch Argus has quite a short flight period from mid-July to early September with a peak in the first two weeks of August when it can be incredibly abundant.

Habitat & Distribution in SW Scotland

Distribution map 2010

The Scotch Argus replaces the Meadow Brown in upland grasslands as the dominant butterfly and it can be locally very common and even abundant with many colonies having hundreds of butterflies and the best sites host thousands.

The Scotch Argus is found in areas of unimproved damp grassland including upland grasslands but in Argyll where the Scotch Argus is the most common butterfly, it is widespread at sea level as well as at altitude. Like other butterflies of unimproved grassland such as the Pearl-bordered, Small Pearl-bordered Fritillary and the Chequered Skipper, the Scotch Argus is most abundant on sunny slopes where birch woodland and bog myrtle provide warmth & shelter and mineral flushing provide an abundance of nectaring sources.

While the Scotch Argus is widespread and abundant in much of Scotland, it will not tolerate improved grasslands or unimproved grasslands with moderate or heavy grazing. Its distribution in SW Scotland reflects this with it being absent from the central belt, coastal parts of Ayrshire and Dumfries & Galloway.


One curious feature of the distribution of the Scotch Argus is that it is present in the north and west (west and east side of Loch Lomond) of the Loch Lomond and Trossachs National Park but absent from the east and south (from Glen Ogle, Strathyre & most of the Trossachs) even though there is suitable habitat. It used to be present in Glen Dochart east of Crianlarich but was not seen here in 2007, perhaps because most of this Glen is now intensively grazed.

There is evidence of a decline in the south and east parts of the range which may be linked to the warmer amd drier summers of the last two decades drying out damp grassland but the Scotch Argus remains a very abundant butterfly in most of Scotland, especially in the west highlands.

Sites in the SW Scotland branch area in which you can see the Scotch Argus include Feoch Meadows (NX263822) in Ayrshire; Glen Douglas (NS268998) in Dunbartonshire and anywhere in Argyll.

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)
  • Kirkland, P. 2005. The Scotch Argus. Butterfly
  • , the magazine of Butterfly Conservation, 89, 23-25.
  • Asher, J., Warren, M, Fox, R., Harding, P., Jeffcoate, G., Jeffcoate, S. 2001. The Millennium Atlas of Butterflies in Britain & Ireland. Oxford University Press.

Written by Andrew Masterman


 
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