Scotch Argus

Scotch Argus Erebia aethiops (Esper 1777) )

Family: Nymphalidae, subgroup Satyrinae (The Browns)

Description

Photos by Iain H Leach

The Scotch Argus looks similar to Meadow Brown, but is darker to the point of being almost black when fresh. Also there are more spots on the upper wings and a figure of eight eyespot on the forewing in closed wing view.

Males are blacker and females are browner. The number of eyespots on the upperwings is variable but usually three in males and four in females.

This butterfly tends to fly only when the sun is shining, but can be active as soon as the sun rises in the early morning. On warmer days males may sometimes fly in duller conditions.

The English population belongs to the subspecies aethiops Esper, the Scottish population to subspecies Caledonia Verity. Scottish specimens are noticeably smaller though it is quite a variable species with over 30 varieties described.

Habitat

The favoured habitat in Cumbria is on carboniferous limestone with mixed grassland and woodland whereas in Scotland the species prefers sunny, sheltered and damp habitats such as tussocky, lightly grazed grassland with scattered scrub or open woodland. Newly planted conifer plantations can also provide suitable habitat, but only temporarily as they will eventually produce too much shade. Open but sheltered areas of moorland are also used in Scotland.

Purple Moor-grass Molinia caerulea appears to be the main foodplant in Scotland, whilst in England Blue Moor-grass Sesleria caerulea is used. Couch Grass Agropyron repens has been recorded at Smardale in Cumbria and other grass species have been noted in Scotland.

Distribution

This species prefers higher areas and covers most of Europe and Asia. It is also found in Scotland. In England there are only two known colonies, both in Cumbria; at Arnside Knott, (National Trust) and Smardale nr Kirkby Stephen (Cumbrian Wildlife Trust).

The species appears to be extinct in Yorkshire although there was one sighting in 2019 on the Dales Way near the Scargill Estate. Previously it used to be found in Upper Wharfdale, especially Grass Wood near Kilnsey. Occasional private releases may have happened in the past and it is also possible that there are still colonies that have not been noticed.

Life Cycle

The eggs are laid singly on blades of grass, which are either part of the foodplant or near it and the greenish-yellow larvae hatch after two to three weeks by chewing out a lid on the top of their egg, leaving just enough to act as a hinge so they can push it up and crawl out. Young larvae feed by day and night and rest at the base of grass clumps when not active. They hibernate in a similar location, usually in the second instar, around October. It is thought that less than half survive winter, possibly due to a mould. The larvae begin to feed again in March, though mainly at night.

Pupation takes place after the fourth instar, at ground level or just below, and involves the construction of a loose cocoon. The adults then fly from late July with the population usually peaking in mid-August. There is a theory that the adults take two years to develop or perhaps a second year is taken if the weather is poor.

Overall this is a species which is poorly understood.

Status

Butterfly Conservation priority: Low

European status: Near threatened

Aberrations


With thanks to the Butterflies of Yorkshire edited by Howard M Frost

Catherine Jones 10/11/20