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Butterfly Conservation- Glasgow & South West Scotland Branch


Holly Blue (Celastrina argiolus)

Description

The Holly Blue is a beautiful little butterfly (wingspan 26-34 mm) commonly found near hedgerows containing holly and/or ivy. The male Holly Blue has all blue upperwings, while the femaleís are blue with black wing tips (this is often more extensive in the second brood). The underwings of both sexes are pale powder blue with small black spots. From a distance the Holly Blue might be confused with the Common Blue, but it tends to be a more active flyer and the underwing markings of the Holly Blue are quite different from those of the common blue, which has orange markings. Both sexes normally rest with their wings closed; only partially opening them to bask in hot sunny weather. The Holly Blue is currently extending its range northwards into south west Scotland.

Credit: Scott Shanks
Credit: Neil Gregory
Credit: Neil Gregory

Life Cycle

After emerging the adults range widely throughout the countryside and donít form true colonies, although they do tend to congregate near areas with Holly and Ivy. The disc-shaped blue-white eggs are laid singly at the base of unopened flower buds of the foodplant and hatch within 2 weeks. In spring, eggs are typically laid on Holly (Ilex aquifolium), whereas the summer eggs are typically laid on Ivy (Hedera helix). Occasionally Bramble (Rubus fruticosus), Dogwoods (Cornus spp.), Gorse (Ulex europaeus), Snowberry (Symphoricarpos alba) and Spindle (Euonymus europaeus) may also used.

The grub-like larva is well camouflaged, and is usually a plain green colour with a dark head. The larva may also have white stripes or areas that are light pink. The larva bores a hole in the side of the flower bud or berries and scoops out the contents, leaving a succession of empty flower buds, each with an access hole in its wake. Itís head is not normally visible as it feeds. The larva can complete can complete their entire life cycle feeding on the terminal leaves of male holly, although female holly plants are preferred. The larva can be found by looking for damage to developing flower buds, where it may then be found attached to a nearby bud. The larva has 4 instars, and the fully-grown larva is approximately 15mm in length. The sepia and brown speckled pupa is formed away from the food plant in deep vegetation and is the the overwintering stage. Like other blues, the larvae and pupae of the Holly Blue are known to produce secretions attractive to red ants (Myrmica spp.) and black ants (Lasius spp). Itís thought that the ants may protect the larvae from attack by the parasitic wasp (Listrodomus nycthemerus) which specifically targets the Holly Blue and can cause high levels of mortality in populations. Parasitism is thought to be at least partially responsible for the cyclical variations in Holly Blue abundance with populations crashing every 6-7 years which in turn leads to lower numbers of the wasp and allows the Holly Blue population to start recovering once more.

Flight Times

In South West Scotland there appears to be two broods per year, as adults have been recorded in late April/May and July/August.

Habitat & Distribution in SW Scotland

Distribution map 2010

The Holly Blue is an strong flyer and ranges widely across the countryside, and consequently can be found in almost any habitat. The species is commonest at sites containing Holly and Ivy such as gardens, church yards, cemeteries and parks. Woodlands can also provide good habitat and the trend of recent decades to little coppicing and poor woodland management which allows the spread of Ivy has probably favoured the Holly Blue and may have contributed to the range expansion in recent decades.

There are very few historical records of Holly Blue in Scotland which is somewhat surprising and it is currently unknown from the Highland branch area although there is a 1966 record from Munlochy, the Black Isle. There is also a 1972 record from Knapdale, Argyll. Most historical records are from Dumfries and Galloway which suggests dispersal from the few colonies in the far north of England,

The Holly Blue is a more active flyer than the Common Blue. In South West Scotland there have been regular sightings of individuals along the Solway coast and breeding has been recorded at Rockcliffe (NX8535). In 2008 there were records of Holly Blues further north, including sightings on 2 consecutive days during August in a garden in Ayr and another in the branch chairmanís garden in Kilmacolm during July.

The Holly Blue has shown a dramatic northwards range expansion since the 1970ís. This may be in response to climate warming with some evidence that populations in Ireland that were single brooded at one time are now producing two broods per year and even a partial third brood in warm sheltered areas in and around Dublin and Cork. The planting of holly in many parks and the neglect of woodlands which has allowed Ivy to become more abundant may also have helped the spread of this species. On the east coast of Scotland the Holly Blue is now resident in the city of Edinburgh and there have also been records from Fife across the Firth of Forth. The Holly Blue seems likely to become more common in south west Scotland if climate warming continues.

References

  • 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. Britainís Butterflies. WILDGuides.
  • Written by Scott Shanks & Andrew Masterman


     
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