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Butterfly Conservation- Glasgow & South West Scotland Branch


Pearl-bordered Fritillary (Boloria euphrosyne) - PRIORITY SPECIES

Description

Similar in appearance to Small Pearl-bordered Fritillary (Boloria selene) but Pearl-bordered Fritillary has an earlier flight period commencing late April to early June while the Small Pearl-bordered flies from late May onwards. 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: Andrew Masterman
Credit: Jim Black
Credit: Jim Black

Life Cycle

The eggs are laid singly on bracken or leaf litter amongst the foodplants, Common Dog Violet or Marsh Violet during May. Ideal habitat is Dog Violet amongst light bracken or bare patches on south-facing hillsides which provide a warm dry micro-climate for the eggs and caterpillars. The caterpillars feed intermittently through the summer and autumn and then hibernate as early fourth instar larvae amongst dead leaves or bracken. In late March, they emerge from hibernation to bask on bracken litter which provides a warm micro-climate in early spring and feed intermittently before pupating after a couple of weeks.

Flight Times

This is the earliest Fritillary being on the wing from late April to early June.

Habitat & Distribution in SW Scotland

Distribution map 2010

In Scotland, the Pearl-bordered Fritillary is associated with a distinct habitat-type which partly explains why this species is quite rare: south-facing hillsides with bracken-grass mosiacs which are often adjacent to open birch woodland. These dry sunny bracken hillsides favour both Dog Violet and Pearl-bordered Fritillary but sites can become unsuitable from birch woodland regeneration, dense bracken growth or coniferisation.

Argyll is an important stronghold for this Priority Species and there are also good colonies in Dumfries & Galloway including at the Mabie Forest Butterfly Conservation reserve (NX9270).

In southern England, the Pearl-bordered Fritillary is more associated with open woodland and has been in decline in recent decades owing to the cessation of traditional coppicing. The situation in Scotland is somewhat better but some sites are in need of management to control the twin threats of birch regeneration and dense bracken growth.

Many sites in Scotland are on Forestry Commission land where this species is confined to wayleaves and forestry tracks. Many forestry plantations are mature now and are being or soon will be harvested. While this process will restore hillsides to more open habitat which in theory would be more favourable for Pearl-bordered Fritillary, the harvesting process may well damage the limited habitat with Dog Violet along wayleaves and forestry tracks and it is unlikely that felled conifer plantations will revert to bracken/grass mosaics without considerable landscaping. So there is concern about the future of Pearl-bordered Fritillary on Forestry Commission land post-harvesting.

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.

Written by Andrew Masterman


 
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