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Butterfly Conservation- Glasgow & South West Scotland Branch

Purple Hairstreak (Neozephyrus quercus)

Description

The Purple Hairstreak is a small woodland butterfly (wingspan 31-40 mm) that is often overlooked (or should that be ‘under-looked’) as it spends most of its life feeding on aphid honeydew in the canopy of oak and ash trees. The male Purple Hairstreak has a beautiful purple sheen to the upper surface of their wings. The upper surface of the female’s wing is predominantly dark brown with only a streak of purple on their forewings. The underwings of both sexes are silvery-grey with a ragged white line and a bright orange and black eyespot at the outer edge. It can be a challenge to get a good view of this butterfly even when you know that a particular oak tree contains a strong colony. Early evening on a warm sunny day is often a good time to look for adults using binoculars or a field telescope… and lots of patience!

Credit: Keith Warmington
Credit: Jim Black
Credit: Jim Black

Life Cycle

The Purple Hairstreak has a single brood per year in South West Scotland. The lifecycle revolves around Oak trees. The adults emerge in July and form colonies focused on prominent oak trees known as the master tree. On warm sunny evenings the master tree becomes the focus of colony activity with individuals flying around the outer branches and occasionally descending to rest on lower vegetation or drink from muddy puddles. Both species of native oaks, the pendunculate oak (Quercus robur) and the sessile oak (Q. petrae) are commonly used as the caterpillar foodplant, but turkey oak (Q. cerris) and evergreen oak (Q. ilex) may also be used. It appears that there is a preference for pendunculate oak in southwest Scotland. The white disc-shaped eggs are laid singly on the tip of an oak twig or at the base of a leaf bud on sunny but sheltered boughs. The egg is the overwintering stage and this photograph shows one at the base of an Oak bud. Interestingly, the larva within the egg is fully developed within 3 weeks, but then becomes dormant until the following April when it hatches. After hatching the reddish-brown larva eats its egg shell before burrowing into a bud to feed protected from predators. From the second instar the caterpillar lives externally, forming a silk web from which it emerges to feed at night. The dark brown pupa is formed either in a crevice in the bark, or on the ground where it may be tended by ants such as the red ant Myrmica ruginodis.

Flight Times

In South West Scotland, the Purple Hairstreak flies from mid July to early September.

Habitat & Distribution in SW Scotland

Distribution map 2010

The Purple Hairstreak requires mature Oak woodland although it can survive for generations on a single tree where neighbouring trees have been cut down. It has also been noted that the ground flora is sparse at many of the oak woodlands where Purple Hairstreak is present with few grasses and little bracken or fern. This may be related to the link with ants which require warm sunny habitats and so this may be a factor which limits the distribution of the Purple Hairstreak. This would be an interesting topic of research in our branch area.

The Purple Hairstreak can be found throughout southwest Scotland from Argyll down to Ayrshire and Dumfries & Galloway. Due to the difficulties in recording this species (it’s found at the tops of trees and is most active in the late afternoon and early evening) the Purple Hairstreak is likely to have a wider distribution and be more abundant than currently shown. The Purple Hairstreak has been seen on some of the western Isles - Arran and Colonsay - demonstrating an ability to disperse which is a characteristic of all butterflies: indeed all insects use the winged adult stage to disperse and colonise new areas.

Colonies can be found in woodland containing mature oaks and can survive for generations around a single isolated oak. There is some evidence of an increase in Purple Hairstreak abundance in English woodlands that have been specifically surveyed for this species. In south west Scotland the Purple Hairstreak is not a species of conservation concern. However, the butterfly does appear to be absent from many oak woodlands, such as those along the Cylde and Avon river valleys where sessile oaks dominate. It is not known why there is a preference for pendunculate oak, but it may relate to the presence of associated ant species, subtly earlier timing of flower and leaf bud development or the concentration of various defence compounds such as anthocyanidins that build up in the leaves as they age.

References

  • Barbour, D., Moran, S, Mainwood, T & Slater, B 2008. Atlas ofr Butterflies in Highland & Moray. Big Sky.
  • Futter, K., Sutcliffe, R., Welham, D., Welham, A., Rostron, A., MacKay, J., Gregory, N., McCleary, J., Tait, T., Black, J. & Kirkland, P. 2006. Butterflies of South West Scotland. Argyll Publishing. (see Atlas page)
  • Asher, J., Warren, M, Fox, R., Harding, P., Jeffcoate, G., Jeffcoate, S. 2001. The Millennium Atlas of Butterflies in Britain & Ireland. Oxford University Press.
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  • Fox, R., Asher, J., Brereton, T., Roy, D., Warren, M. 2006. The State of Butterflies in Britain and Ireland. Pisces Publications.
  • Thomson, G. 1982. The Butterflies of Scotland. Croom Helm London.
  • Tomlinson, D. & Still, R. 2002. Britain’s Butterflies. WILDGuides.
  • Written by Scott Shanks & Andrew Masterman


     
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