Photo above top left by D O'Brien (also header photo)

Photo above top right by RD Burton

Photo above middle by Samantha Batty

The Pearl-bordered Fritillary is the first of Yorkshire’s four Fritillary species to emerge and normally does so mid-late April. The species is medium sized; its upper wings bear orange and black patterns of dots and ribbons while its underside bears two large silver “pearls”. These, along with seven outer “pearls” with their adjacent reddish chevrons, help to distinguish it from its later flying congener, the Small Pearl-bordered Fritillary (Boloria selene). The flight periods of these species do overlap and both species co-exist on at least one of Yorkshire’s sites meaning identification may be problematic.

Males fly close to the ground, often for prolonged periods as they search for unmated females. Once mated, the females are less readily seen; they settle more often than the males and crawl upon ground vegetation looking for locations in which to lay their eggs. Adults are opportunistic feeders and will utilise a variety of spring flowers including Bugle, Ground Ivy, Dandelion and Bluebell; when nectar sources are scarce Blackthorn blossom is sometimes used, usually at a very early stage of the flight period before other flowers are available.

This species can only breed where microclimatic conditions are sufficiently warm for its larvae to develop. Yorkshire’s few surviving sites are well drained mosaics of limestone grassland, Bracken, patchy scrub and Bramble. Its main larval host at these sites is Common Dog Violet. Hairy Violet is also present at two sites although the extent to which the butterfly uses the latter is not known. The presence of dead Bracken litter is of critical importance for the species on our sites and at many others too; the temperature of sunlit Bracken litter may exceed that of adjacent grassy areas by as much as 20C. These superheated conditions promote rapid larval growth.

Elsewhere in the UK the species breeds in woodlands. In Scotland, scattered woodlands suffice whereas those in England more often require frequent management such as coppicing if they are to remain suitable. In both cases, abundant violets and dead plant litter are essential habitat components.

In Yorkshire, the Pearl-bordered Fritillary remains confined to a small network of sites located close to Kirkbymoorside. In 2011, following extensive cutting of scrub and Bramble, the species recolonised a former site from which it was lost a decade earlier. At about the same time it also appeared in woods near Pickering but has since died out following rapid regeneration of the clear fell site that it had colonised (whether this colonisation was human-assisted remains a moot point). Barring these minor expansions, the species has been confined to this network for many years. It was once slightly more widespread in Yorkshire though never common (see Frost, 2005 for details). Most if not all of former locations listed are no longer suitable for the species.

Elsewhere in the UK the species’ Scottish distribution extends from Mull and the Argyll coast in the west to Deeside and the Sutherland coast in the east. It is also present in Dumfries and Galloway. In Wales, it is found in several landscapes including the South Ceredigion Coast, the Border Hills and on the Clwydian Limestone. Elsewhere in England it occurs in the Morecambe Bay Limestones, South Cumbria Low Fells, Devon and Cornwall, central southern England and into parts of the south-east. Further north, it also occurs in the Oswestry Border Hills and in the Wyre Forest.

The species is single brooded in Yorkshire. Adults are normally on the wing from mid-late April to early June with the butterfly emerging roughly a week earlier on our south-facing sites than it does at our other which slopes towards the north east.

Eggs are laid singly, usually on dead Bracken or leaf litter near to violets, though a few are laid on the host plant itself. Larvae hibernate amongst dead leaves or Bracken whilst still quite small and emerge in early spring when they spend much of their time basking on dead litter, interspersed with short bouts of feeding. The selection of warm, dry habitats and the basking behaviour of larvae enable them to develop rapidly even in cool spring weather. Pupae are formed amongst leaf litter and adults emerge after a few weeks.

The species is amongst Yorkshire’s rarest breeding butterflies. It is confined to only a handful of sites and there is currently little suitable habitat to which it might spread. The species is therefore extremely vulnerable, both to deterioration of habitat quality and to direct impacts such as off-road motorcycling. None of the sites it occupies are afforded statutory protection therefore their protection and management owe much to continuing goodwill of the owners. Most sites are monitored annually; butterfly numbers are currently stable and may even have increased slightly during the last two decades.