Despite its name, the Scotch Argus is not only found in Scotland; it is also found at two sites in the north of England. A freshly-emerged Scotch Argus is a sight to behold, the dark brown velvety uppersides making the butterfly appear almost jet black from a distance. The butterfly is unmistakable when seen basking with its wings open, when orange bands containing distinctive spots are revealed. This butterfly lives in well-defined colonies that are often very large.
Like the Mountain Ringlet, the ability of this butterfly to survive cool temperatures means that it was probably one of the first species to recolonise the British Isles after the last ice age, over 10,000 years ago. The English colonies, Arnside Knott and Smardale Gill, are both found in Westmorland. Colonies are much more numerous in Scotland, where this butterfly can be found in most of northern, western and south-west Scotland. This butterfly is absent from the lowlands of central Scotland, many of the western isles (including the Outer Hebrides), Orkney and Shetland.
A colony at Grassington in Mid-west Yorkshire, famous for a particular race that had reduced orange markings, became extinct in 1923. According to Dennis (1977) "This colony which used to occupy parts of Grass Wood was last observed by Clutten in 1923. The orange markings on the upperside of the males were nearly obsolete; and this feature in the females was scarcely better developed than in ordinary males".
This species was first defined in Esper (1777) as shown here and as shown in this plate (type locality: Southern Germany). The nominate subspecies is found in England and the north-east of Scotland.
Erebia aethiops ssp. caledonia
This subspecies was first defined in Verity (1911a) as shown here and as shown in this plate (type locality: Galashiels, Scotland). This subspecies is found in western and south-west Scotland although its distribution with regard to the nominate subspecies is by no means clear cut. The distribution shown here is taken from Thomson (1980). This subspecies differs from the subspecies aethiops as follows:
1. Invariably smaller size.
2. Forewings narrower and more elongated, with sharper angles and a straighter wing edge.
3. The reddish yellow band is narrower and never contains more than three small eye spots.
4. The bands on the underside of the hindwings are frequently indistinct.
Erebia aethiops ssp. caledonia (Verity, 1911)
Original (French)Se distingue bien de la race alpine par sa taille toujours moindre (envergure : 33-42 mill., tandis que celle du type varie entre 40 et 45 mill.), par ses ailes bien plus étroites et allongées, avec les angles plus aigus et le contour du limbe plus droit; la bande fauve est étroite et ne contient jamais plus de trois petits ocelles, tandis que chez la race alpine elle en contient souvent quatre ou cinq, surtout chez la ♀; enfin les bandes du revers des postérieures sont assez fréquemment peu distinctes.Habitat. - La série typique de ma collection, que je décris, est de Galasliiels (Écosse). Dans d'autres régions écossaises volent des formes de transition au type alpin.TranslationClearly distinguished from the alpine race by its invariably smaller size (wingspan : 33-42 mm., while that of the nominate form varies between 40 and 45 mm), its narrower and more elongated wings, with sharper angles, and by the straighter wing edge; the reddish yellow band is narrow and never contains more than three small ocelli, while in the alpine race there are often four or five, especially in the female; finally, the bands on the underside of the hindwings are frequently indistinct.Habitat: The type series in my collection, which I am describing, is from Galashiels (Scotland). In other parts of Scotland forms transitional to the Alpine type fly.
The flight period is fairly short for a butterfly that can appear in significant numbers. Butterflies emerge at the end of July, peaking in early August, with a few individuals surviving into September. There is one generation each year.
Erebia aethiops ssp. aethiops
Erebia aethiops ssp. caledonia
The chart(s) above have been correlated with the phenology plot below, taken from the UK Butterfly Monitoring Scheme. The blue line gives average counts over the full data set from 1976 to date, and the red line gives the average for the last year.
Most colonies are found in sheltered and damp areas. Bogs, woodland edges and riverbanks where the foodplant grows are typical habitats. The English colonies are situated in a different type of habitat, where sites are limestone grassland sheltered by adjoining woodland.
The primary larval foodplants are Blue Moor-grass (Sesleria caerulea) and Purple Moor-grass (Molinia caerulea).
Adults feed primarily on Devil's-bit Scabious (Succisa pratensis), Field Scabious (Knautia arvensis), Heather (Calluna vulgaris / Erica spp.), Knapweeds (Centaurea spp.), Marjoram (Origanum vulgare), Ragwort (Senecio jacobaea) and Thistles (Cirsium spp. and Carduus spp.).
The adults are often the first butterflies of the day to be seen at suitable sites, their dark brown wings presumably allowing them to warm up more quickly than other species. They fly only when the sun is shining, and tend to retreat among grasses as soon as clouds appear, their undersides closely resembling a dead leaf. They reappear as rapidly when the sun comes out again and it is fascinating to watch an apparently-barren grassland come to life with butterflies as the clouds move away. Both sexes feed from a variety of nectar sources.
Males adopt both perching and patrolling strategies when in search of a mate. Males will fly for long periods when patrolling, searching out any dark brown object that is a potential mate. Females are mated shortly after they emerge with no discernable courtship involved, and the pair remain coupled for a few hours.
When egg-laying, the female selects sites that are in full sunshine and that are sheltered. She will bask for a while before crawling down into the grass and laying a single egg either on the grass or on nearby vegetation or debris. Eggs tend to be laid on Purple Moor-grass in Scotland and Blue Moor-grass in the Lake District.
Erebia aethiops ssp. caledonia
Description to be completed.
Click here to see a full list of aberrations for this species.
ab. freyeri (Oberthur.Lep.Comp.1911.5.(1).p.328.pl.LXXIII.f.674. & Lep.Comp.3.p.326.(described but not named.))= pentaocellata Rocci.Mem.Soc.Ent.It.1923.2.p.8.
Forewing with five ocellated spots in the red band, all pupilled with white. Hindwing with four similar spots. Oberthur describes and figures this form but also mentions a more extreme form figured by Freyer in Neu Beitr.pl38.f.2. which has six ocelli on the forewing. Since Oberthur figures the five-spotted form it must be taken as freyeri, the six-spotted form has since been named croesus.
The spherical eggs are yellow when first laid, but turn light brown after a few days. This stage lasts between 2 and 3 weeks.
When emerging from the egg, the larva nibbles around the top of the egg, but leaves a hinge, essentially creating a lid that it then opens. The eggshell is then partly eaten. Larvae feed during both day and night, but development is slow. Larvae hibernate while in the 2nd instar in leaf litter at the base of the foodplant. They emerge in the spring and mature larvae feed only at night, resting in ground debris during the day. There are 3 moults in total.
The pupa is formed in a loose cocoon, typically in mosses or some other soft material. This stage lasts between 2 and 3 weeks.
Description to be completed.
Click here to see the distribution of this species overlaid with specific site information. Alternatively, select one of the sites listed below.
|Airhouse Quarry, Alemoor West Loch and Meadow SSSI, Allt Mhuic Nature Reserve, Arnside Knott, Auchalton Meadow, Balnaguard Glen, Ben Vrackie, Big Wood, Boat of Garten, Cambus O'May, Craigellachie National Nature Reserve, Craigower Hill, Culbin, Dunhog Moss SSSI, Eildon Hills, Ettrick Haughlands, Feshie Bridge, Glasdrum Wood, Glen Fionnlighe, Glen Loy, Glen Nevis, Glenlivet, Hare and Dunhog Moss, Hartwoodmyres, Hightae Mill Loch, Invermoriston, Inversnaid, Keltneyburn, Knowetop Lochs, Lein of Garmouth, Lindean Reservoir SSSI, Loch an Eilean, Lynachlaggan Birchwood, Roughlee, Shian Wood, Smardale Gill, Tummel Shingle Islands, Whitlaw Mosses NNR, Yair Hill Forest|
Despite experiencing a long-term decline in its distribution, this butterfly has increased at monitored sites and is not, therefore, currently a priority species for conservation efforts.
The table above shows the distribution and population trends of species regularly found in the British Isles. The distribution trend represents a comparison between data for the periods 1995-1999 and 2005-2009. The information provided is taken from the Butterfly Conservation report The State of the UK's Butterflies 2011. The UK BAP status is taken from the UK Biodiversity Action Plan (UK BAP) (2007 review).
The following links provide additional information on this butterfly.
The species description provided here references the following publications: