Friday, 9 May 2014

Spring pearls ...

Pearl-bordered Fritillary (Boloria euphrosyne)

This beautiful woodland butterfly occurs in scattered and isolated colonies south-west of a line running between Denbighshire in the north-west to East Kent in the in south-east. There are also colonies in Westmorland and West Lancashire. It is also widespread in central Scotland, but very local or absent in the north and south of the country. In Ireland, it is found in the Burren limestones of Clare and southeast Galway. It is absent from the western and northern Isles of Scotland, the Isle of Man and the Channel Islands. B. euphrosyne survives in West Sussex thanks to carefully managed Sweet Chestnut coppice in several important woodlands which allows the Common Dog-violet (Viola riviniana), the main larval foodplant, to grow in appropriate conditions.

This is the earliest of our fritillaries to emerge. In good years, the butterfly emerges at the end of April in the south. Most adults emerge at the start of May, but may not appear until the end of May in more northerly locations.

B. euphrosyne is typically found in deciduous woodland containing open areas, such as woodland clearings, that provide the right conditions, foodplants and nectar sources for this species to survive. Suitable sites are generally habitable 2 to 4 years after a woodland clearing has been formed, when the foodplants and nectar sources are optimal for this species. However, these sites can quickly become overgrown and, unless there is suitable habitat nearby or regular habitat management undertaken, colonies are often lost.

Larvae feed by day and generally rest in leaf litter, but can also be found, especially after hibernation, basking on dead bracken. They eat the entire leaves, leaving just the stem intact. They will also feed on only the leaf lobes, at the base of the leaf, leaving characteristic feeding damage that can give away the presence of a nearby larva. After moulting for the third time the larva enters hibernation, generally in a dried leaf, emerging in the spring to complete its growth. There are 4 moults in total.

The two images show a male, referable to ab. interligata, Cabeau (1919) + ab. transversa, Vorbrodt (1911) recently found in West Sussex.

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