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Butterfly Conservation- Glasgow & South West Scotland Branch


Large Heath (Coenonympha tullia) - PRIORITY SPECIES

Description

The Large Heath is a small highly variable orange-brown butterfly (wingspan 35-40 mm) of wet acidic moorland, bogs and heath. In south west Scotland there are two forms of the Large Heath. The subspecies polydama is the most common, with orange-brown coloured underwings with white-ringed eyes spots. The sub species scotica is found in the western isles and the northern half of the mainland with local populations in Dumbartonshire and Stirlingshire. The scotica sub spp is a bit larger and has much paler underwings appearing pale grey rather than dark grey and has smaller eyespots.

Some specimens of scotica sub spp can look very similar to Small Heath but such ambiguous individuals can be distinguished using the following logic: the eyespot on the underside of the forewing is within a paler band of colour in the Small Heath, while it is closer to the edge of the wing outside the pale band in the Large Heath; the pale white patch in the middle of the hindwing is rounded in the Small Heath and more pointed in the Large Heath; and the hindwing of the Large Heath tends to have more gradual shading towards the edge than the Small Heath. Both sexes are similar in appearance, although the female may be slightly larger. The pale orange upper wings of the large heath are almost never shown, as the wings are held shut at rest.

Credit: Andrew Masterman
Credit: Jim Black
Credit: Scott Shanks

Life Cycle

The Large Heath has a single brood in South West Scotland. The adults begin to emerge from mid June and set about finding mates within their colony. The adults are highly sedentary, rarely moving more than 100m during their lives. The pale yellowish eggs are laid singly on dead stems at the base of tussocks of the larval food plant Hairís-tail Cotton-grass (Eriophorum vagunatum) and occasionally on Common Cotton Grass (Eriophorum angustifolium). The green caterpillar has a dark green stripe along itís back and develops slowly throughout the summer and autumn before hibernating at the base of the grass tussock. Feeding resumes during warm days in spring, before forming a green pupa suspended from grass stems in late April or May. In the north of Scotland and in some upland areas a small proportion of larvae have a two year life cycle and hibernate a further year as larvae. This is thought to be a survival strategy to cope with harsh and unpredictable weather conditions that can occur during the adult flight period.

Flight Times

In South West Scotland the Small Heath can be found on the wing from mid June to early August, with a peak in sightings during early July. The butterfly has a gentle bobbing flight as it moves above tussocks of Hairís-tail cotton-grass, the larval food plant. The adults frequently stop to nectar at the flowers of heather and cross-leaved heath.

Habitat & Distribution in SW Scotland

Distribution map 2010

The habitat of the Large Heath is open, wet areas where cotton grass is abundant such as damp acid moorland, raised bogs and blanket bogs in upland areas. Plants such as Sphagnum moss and Cross-leaved Heath together with the foodplant, cotton grass, are characteristic of good Large Heath habitat. In Scotland, there are large areas of such habitat away from urban areas and the agricultural lowland areas and the Large Heath is a widespread but local species but it is seldom seen in large numbers. Highest populations occur in Caithness & Sutherland and it is known from most of the western Isles including Ailsa Craig, Arran, Islay, Jura, Mull, Lewis and Skye and is also found on Orkney but not Shetland.

The Large heath was designated a UK BAP priority species in 2007 owing to big declines in central and eastern England where intensive agriculture has destroyed the bog habitats which this butterfly inhabits. Neither lowland raised bogs nor upland moorland bogs are valued by landowners so are vulnerable to changes in landuse such as drainage to convert to arable land or recreational uses such as golf courses. In Scotland, large areas of upland moorland bog have been planted with conifer plantations which has undoubtedly adversely affected some populations of the Large Heath.

The Large Heath can be found throughout south west Scotland but there are few known colonies through the central belt and Glasgow area. However, many known colonies are threatened by habitat fragmentation and the poor dispersal ability of this species means that it is susceptible to local extinctions. The large-scale drainage of bog sites, commercial peat extraction and the afforestation of moorland has resulted in the loss of many colonies, while overgrazing by sheep in some areas may also have lead to the loss of this species. Management of sites for Large heath includes maintaining large connected areas supporting the food plant, reducing grazing regimes, and if the water table needs to be restored at bog sites, it is important to prevent prolonged flooding which can kill hibernating larvae.

References

  • Barbour, D., Moran, S, Mainwood, T & Slater, B 2008. Atlas ofr Butterflies in Highland & Moray. Big Sky.
  • 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.
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  • Fox, R., Asher, J., Brereton, T., Roy, D., Warren, M. 2006. The State of Butterflies in Britain and Ireland. Pisces Publications.
  • Thomson, G. 1982. The Butterflies of Scotland. Croom Helm London.
  • Tomlinson, D. & Still, R. 2002. Britainís Butterflies. WILDGuides.

Written by Scott Shanks and Andrew Masterman


 
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