Purple Hairstreak (Neozephyrus quercus)

Peak District local information

When to see: July-September

Where to see: Anywhere with the presence of Oak trees

Behaviour: Perch

Wingspan: 31-40mm

Caterpillar food plant: Pedunculate Oak (Quercus robur) and Sessile Oak (Quercus petraea)

Peak District status: This butterfly is closely linked to the presence of oak trees, on which the larvae feed. It is a very recent colonist of the Peak District, following rapid northward expansion of its national range. It was recorded for the first time in 1995, at two localities on the southwest and northeast edges of the National Park. By the end of 2004 the number of recorded localities had risen to about 25, distributed widely across the Peak District, though so far none has been reported in the White Peak . Recorded sites include the Ladybower area, Longdendale Valley , Glossop, Goyt Valley , Lyme Park , Padley Gorge and Kinder River Valley . The more or less simultaneous appearance of purple hairstreaks on both sides of the Peak District indicates that colonisation has occurred from both east and west.

In Longdendale and the upper Derwent Valley there is some evidence of range expansion into more scattered clusters of trees and there is still substantial scope across the area for infilling and further range expansion into unoccupied woods and small groups of oaks. Purple hairstreaks are difficult to see and to record and they are probably overlooked at many sites, especially where they occur at low density. On the other hand, it is not known whether all the colonies recorded so far have persisted, so the current overall trend in the Peak District is unclear. It also remains to be seen whether such small and relatively isolated populations will remain viable in the long term and their continued existence in these habitats may depend on a continuation of warmer climate trends.

Several Peak District sites are upland oakwoods, some of which reach an altitude of 300m on the moorland edge. These typically consist predominantly of sessile oak (Quercus petraea) with some Q. robur, together with hairy and silver birch (Betula pubescens and B. pendula), rowan (Sorbus aucuparia) and occasional holly (Ilex aquifolium) and other species. The understorey is generally absent or sparse and the field layer is mainly composed either of dwarf shrubs (heather, bilberry) or wavy hair grass Deschampsia flexuosa. Bracken Pteridium aquilinum is frequent. As a result of poor, mainly acid soils, steep slopes, altitude and exposure many trees are stunted or crooked and the canopy is low and open. Some other woods (e.g. Padley Gorge, Goyt Valley and Kinder Bank Wood) are more extensive and varied, with an admixture of later plantings of other tree species. The occurrence of purple hairstreaks in small upland oakwoods appears to be a new phenomenon in England , although its distribution in Ireland is restricted to hillside oakwoods in the south (Emmet and Heath 1989).

The upperwings in both sexes are very dark, with a purple sheen visible in the right light; in males the purple extends over both wings, in the female it is restricted to a patch on the forewing. The underwings are a pale silvery grey, with a white streak and a small orange spot next to the short ‘tail’. The latter features can only be observed close to or through binoculars - an adult basking on an oak leaf can occasionally be picked out by carefully scanning the canopy. Purple hairstreaks spend most of the time in and around the tree tops, rarely descending to feed on flowers and a special effort is required to observe and record them. One of the best methods is to watch for its silvery spinning flight above the canopy in the late afternoon sun.

Many recorded purple hairstreak sites in the Peak District are Derbyshire Wildlife Trust reserves or are situated in SSSIs or are in sympathetic land ownership (National Trust, Peak District National Park Authority). Upland oak woodland is also a priority habitat under the UK Biodiversity Action Plan, with national targets for the expansion of the area covered. A number of conservation initiatives aim to conserve and enhance the surviving oak woodland. Most, but not all, the remaining Peak District oakwoods are fenced to exclude sheep grazing and thus allow natural regeneration, while active planting schemes, using locally-sourced acorns, have been used to increase the area of oak woodland at two DWT reserves.

 

Purple Hairstreak butterfly