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Butterfly Conservation- Glasgow & South West Scotland Branch

Small Pearl-bordered Fritillary (Boloria selene) - PRIORITY SPECIES

Description

Similar in appearance to Pearl-bordered Fritillary (Boloria euphrosyne) but Small Pearl-bordered Fritillary has a later and longer flight period commencing late May, peaking in June with some individuals flying in July or even early August while the Pearl-bordered flies from late April to mid-June. Both are medium-sized bright orange butterflies with similar markings on the upper wings except for the black chevrons on the upper forewing being more separated from the dark border in Pearl-bordered but joined to the dark border in the case of Small Pearl-bordered. The different markings on the under hind-wings are the best method of distinguishing between these two species. The Pearl-bordered Fritillary has a small dark spot near the base of the hind underwing with two silver/pearl white cells on either side and a generally tawny appearance and the white outer cells are bordered by brown chevrons. The Small Pearl-bordered Fritillary has a larger black spot near the base of the hindwing surrounded by seven silver/pearl white cells which are bordered by black as are the white cells on the margins of the hindwing. Caution is required though as Small Pearl-bordered Fritillaries are very variable and worn individuals can look very similar to the much rarer Pearl-bordered Fritillary.

Credit: Anon
Credit: Jim Black
Credit: Jim Black

The insularum subspecies which has a large amount of white on the underwings occurs in the SW Scotland branch area. Sexes can be distinguished by the smaller two white patches at the base of the underwing in males compared with females.

Life Cycle

The eggs are laid singly on Marsh Violet in damper habitats and on Dog Violet in drier habitats. The caterpillars hatch in mid-summer and feed through the late summer and autumn and then hibernate as early fourth instar larvae amongst leaf litter. In the spring, they emerge from hibernation to continue feeding on violet leaves. In early May, they pupate suspended on vegetation just above ground level.

Flight Times

The earliest individuals used to emerge in early June but over the last ten years, the warmer temperatures have resulted in some individuals flying in the last week of May. While June is the peak flight period, some individuals may be seen through July and into early August with even a few stragglers seen in September.

Habitat & Distribution in SW Scotland

Distribution map 2010

The Small Pearl-bordered Fritillary is much more widespread in Scotland than the Pearl-bordered but it is found in abundance on many Pearl-bordered Fritillary sites indicating that these two species have somewhat similar habitat requirements. Both are found on sunny south-facing bracken/grass hillsides with open birch woodland. However, the Small Pearl-bordered Fritillary prefers wetter habitats than the Pearl-bordered in Scotland, namely damp grassland and moorland (up to 400m or so). In open grassland and moorland, low numbers are found but in sunny sheltered areas, large populations can occur, especially where mineral enrichment from flushing or run-off promotes vigorous growth of Marsh Violet.

This preference for sites with sunshine and shelter means glades or wayleaves within deciduous or coniferous woodland are favoured habitats for Small Pearl-bordered Fritillary but such sites become unfavourable with time unless scrub regeneration is controlled.

In 2007, Pearl-bordered Fritillary was designated a UK BAP species owing to its continued decline in lowland England where damp grasslands have been ploughed up during the 20th century for intensive agriculture confining it to woodland glades. Like the Pearl-bordered Fritillary, it has also been adversely affected by the cessation of woodland coppicing during the 20th century which used to provide a succession of sunny woodland glade habitats. But in Wales, northern and western England and Scotland where Small Pearl-bordered Fritillary is associated with damp grassland and moorland which are still widespread, populations are more stable

The SW Scotland branch area is an important UK stronghold for the Small Pearl-bordered Fritillary as it is locally common in some areas such as Dunbartonshire, Dumfries & Galloway and Argyll. But it has also shown local declines such as in Greater Glasgow and it is currently part of a local biodiversity action plan in Glasgow, East Dunbartonshire & North Lanarkshire. It is perhaps a good indicator of unimproved land such that this butterfly is seldom seen in the lowland agricultural areas of Scotland.

Action taken to conserve the much rarer Pearl-bordered Fritillary should benefit the Small Pearl-bordered too, and in particular the maintenance of sunny woodland glades within either deciduous or coniferous woodland will ensure these two beautiful bright orange butterflies survive in the SW Scotland branch area.

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.

 
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