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Butterfly Conservation- Glasgow & South West Scotland Branch


Large White (Pieris brassicae)

Description

The Large White is our largest white butterfly (wingspan 58-63 mm). It is commonly known as the Cabbage White by gardeners for its habit of laying large batches of eggs on cultivated brassicas such as cabbages. The female has two black spots on its upper forewings and is larger than the male which has unspotted forewings. The female also has more yellow on the underside of her wings than the male. Both sexes have black tips to their forewings which extend further down the outer edge of the wing than in the Small White and black spots on the underside.

Credit: Jim Black
Credit: Scott Shanks
Credit: Scott Shanks

Life Cycle

The adults emerge from mid April and set about finding mates. Two broods are generally produced each year. Females are strongly attracted to the mustard oils produced by plants of the brassica family. Clusters of 50 or more yellow rugby-ball shaped eggs are laid on the underside of the leaves of cultivated varieties of Cabbage and Brussels-sprouts (Brassica oleracea), Oil-seed rape (B. napus), nasturtium (Tropaeolum majus) and wild mignonette (Reseda lutea). At coastal sites sea kale (Crambe maritma) may be used. The black spotted green and yellow caterpillars are gregarious and can quickly defoliate the food plant which can be a serious problem for organic brassica farmers and gardeners! The butterfly doesn’t get it all its own way however, as the large concentration of caterpillars attract predators and parasites such as the wasp Cotesisa glomerata who’s larvae develop inside the caterpillar and kill their host when they emerge. This can result in large population swings observed in this species. The pale yellow and black speckled pupa is the overwintering stage and is often formed on walls, fence posts or inside sheds or garages. An interesting quirk of the Large White is that the pupae may be suspended horizontally as an alternative to the normal upright position of the Whites which is maintained by the cremaster being attached to a silken pad at the bottom and by a silk girdle around the middle of the pupa higher up. In the horizontal position, this silk girdle again maintains the pupae in its position.

Flight Times

In South West Scotland adults can be found on the wing from April through to early October, with numbers peaking in June and then again in August through to mid September. The local population is augmented by migrants from Europe each year which have a strong urge to fly north and reach all parts of Scotland including Orkney & Shetland.

Habitat & Distribution in SW Scotland

Distribution map 2010

The Large White does not form discrete colonies but is a highly mobile and can be found almost anywhere in South West Scotland. It is most common in urban areas in parks & gardens owing to the presence of its foodplants in gardens and along the coast. The growing of Nasturtiums may also attract Large White to gardens.

As with the Small White, crops of oilseed rape are also a foodplant and populations of Large White are associated with them such that the distribution of the Large White in SW Scotland is similar to that of the Small White with highest densities occurring in the arable areas of central Scotland and coastal areas of Ayrshire and Dumfries & Galloway where oilseed rape crops occur.

Migrants from the continent augment the Scottish population, particularly in late summer, but the number of migrants varies a lot from year to year. In years with few migrants, the Large White can be quite scarce in Scotland. Purple flowers such as knapweed, thistles, lavender and buddleia tend to be the favoured nectar sources.

Up until the middle of the 20th century, peak populations of the Large White tended to be higher and it is thought that migrations from the continent are smaller now due to the use of insecticides on Brassica crops, more intensive farming and land use changes reducing habitat on the near continent.

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.
  • 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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