Green Hairstreak (Callophrys rubi)
Peak District local information
When to see: May-June
Where to see: Moorland
Caterpillar food plant: Bilberry (Vaccinium myrtillus)
Peak District status: This hardy little butterfly is one of the earliest species to emerge in the Peak District and the only one that is more common in moorland areas than elsewhere. It is widely distributed across the Dark Peak where it favours sheltered cloughs and slopes that contain a good growth of its main larval food plant, bilberry (Vaccinium myrtillus). It can also be found along moorland roads and lanes with a narrow fringe of dense bilberry and where south-facing drystone walls provide a warm microclimate. It generally avoids areas where the bilberry has been cropped short by sheep. Where bilberry is absent, green hairstreaks may be found on gorse, sometimes on isolated patches of bushes in areas of heavily grazed grass. Males often use hawthorn trees and other shrubs as a perch to look out for females. It has been recorded up to 500m, though it is usually seen at lower altitudes. Green hairstreaks also occur in the limestone dales of the White Peak , but in much smaller numbers. Alternative food plants there include common rock rose and bird’s foot trefoil.
The adults normally emerge towards the end of April or in the first few days of May, depending on conditions. In the exceptionally warm and sunny spring of 2003, Green Hairstreaks were seen in the first week in April. They remain on the wing until mid-June, very rarely extending into July. Colonies are usually small but some reach 50 or more.
It always perches with its wings closed and its bright green underwings are unmistakable, though not always easy to pick out against the background of bilberry or crowberry on which it spends much of its time. The brown upperwings make it fairly inconspicuous in flight. Males and females are more or less identical.
Moorland fires pose a potential threat to the habitat and to the butterfly itself at the egg and larval stages. Heavy grazing suppresses bilberry and prevents it from flowering and may even remove it altogether, to be replaced by grass. Overgrazing by sheep has considerably reduced the area of moorland in the Peak District over recent decades. Fortunately, several government agri-environment programmes such as the Environmentally Sensitive Area scheme and Countryside Stewardship Scheme include measures to lower livestock densities.
Many green hairstreak sites enjoy some kind of protected status. A very large proportion of the Peak District moorlands are covered by four Sites of Special Scientific Interest ( Dark Peak , Eastern Peak District Moors, Goyt Valley , and Leek Moors). Large areas are in addition under sympathetic land management, such as the National Trust’s High Peak Estate and the Eastern Moors estate owned by the Peak District National Park Authority. Both of these contain numerous colonies. In the White Peak , many known green hairstreak sites are in the Derbyshire Dales National Nature Reserve, Plantlife’s Deep Dale reserve, Derbyshire and Staffordshire Wildlife Trust nature reserves and Sites of Special Scientific Interest. Upland heath is a national priority habitat under the UK Biodiversity Action Plan. Several initiatives to promote moorland conservation and restoration through measures such as grazing reductions, a decrease in the extent of burning and re-seeding of areas of bare peat are being implemented by English Nature, Peak District National Park, National Trust and other organisations.