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Duke of Burgundy in Cumbria

By Peter Wilde

Duke of Burgundy Fritillary Credit Peter WildeThere are fewer than 200 colonies of this charming little butterfly left in Britain. Most of them are small, which means that the total UK population is likely to be smaller than many other species considered to be much rarer. The key strongholds of the species are in central southern England, with isolated outposts in the east Midlands, North Yorkshire Moors and at the head of Morecambe Bay. There are fewer than 10 colonies left on the limestone of Morecambe Bay in south Cumbria and north Lancashire. The flight period is usually for about one month from mid-May.

Historically this was a woodland species. Colonies moved into new areas as they were cut, dying out in other areas as they became overgrown. As woods ceased to be managed and coppiced after World War I, the species sought out limestone and chalk grassland sites. This trend was accelerated in the 1950's and 1960's as myxomatosis decimated rabbit numbers and the swards got longer. As with the marsh fritillary, the biggest colonies are now found on land owned by the Ministry of Defence on Salisbury Plain.

The sites occupied round Morecambe Bay are on the whole different from those in the rest of the country as they occur mostly on limestone pavement which is ungrazed and has little grass cover.

EgDuke of Burgundy Credit Peter Wildegs are laid on the underside of primula leaves; cowslip is preferred to primrose. The plants are chosen with great care - the female Duke of Burgundy has the uncanny knack of knowing which plants are not going to dry out as the larvae develop. Thus the plants chosen have leaves 8 - 10 cm long and are likely to be partly shaded by a clump of grass or over-hanging bush, whilst remaining in the warmth of the sun. Finding the perfect spot presents a particular challenge on the limestone of Morecambe Bay because it can get incredibly hot, with many primula plants quickly turning yellow in dry spells of weather.

Keeping habitat in prime condition for this species poses considerable difficulties. On grassland sites the optimum grazing seems to be autumn grazing by cattle. Sheep crop the sward too close and the primulas become exposed - the species must have shelter and warmth. No grazing allows scrub to develop, eventually shading out the foodplant. Cattle are particularly good at disturbing the ground - cowslip needs fresh disturbed earth on which to germinate. Unfortunately grazing isn't an option at the best Morecambe Bay sites, so "human grazing" by dedicated butterfly conservationists is likely to continue to be necessary to prevent them getting overgrown.

Female Duke of Burgundy butterflies stay hidden for much of the day, although research suggests that they will travel up to 5 km in search of suitable habitat. The key here is that there must be natural corridors along which they will move - too often modern agriculture provides a barrier - and it is the failure to create new colonies, rather than loss of old colonies, that puts this species under so much threat.


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