Migration

The migration of butterflies and other insects, over hundreds or even thousands of kilometers, is a remarkable feat. The most famous example is the travels of the Monarch butterfly, Danaus plexippus , that aggregates over winter in great numbers in a small area of Mexico, yet the adults produced in the following spring migrate as far north as Canada.

The definition of migration is not simple. The seasonal two-way movement of individual birds between breeding and overwintering locations is the typical image of migration held by many naturalists. However, in the case of butterflies, individuals do not, except by chance, return to the areas in which they were born, whereas birds may do so year after year.

For butterflies, and other insects, we use a definition of migration based on geographic boundaries rather than on the behaviour of the insects, e.g. migrant butterflies are considered to be those in which numbers in the UK depend (or are believed to depend) to a large extent on immigration from abroad.

The most unequivocal migrants are those butterflies which breed in Britain but overwinter here so rarely that the contribution to the following year's population is negligible. The three most common of these migrantory butterflies are the Red Admiral , Painted Lady and Clouded Yellow , in declining order of average frequency. Although individual red admirals have been known to hibernate in Britain, this is still probably a rare occurrence.

Another group of butterflies is known to range widely over large areas of countryside and some of these have been seen in large numbers, apparently on migration, at sea or on the coast. This group includes the Peacock and Small Tortoiseshell , but paramount amongst them are the Large and Small white butterflies.

To find out more about what butterfly transect data tells us about migrants see the following publications:

Pollard, E. (1982) Observations on the migratory behaviour of the Painted Lady butterfly, Vanessa cardui (L.) (Lepidoptera: Nymphalidae). Entomologist's Gazette, 33, 99-103.

Pollard, E., Hall, M.L., & Bibby, T.J. (1986) The clouded yellow migration of 1983. Entomologist's Gazette, 227-234.

Pollard, E., Van Swaay, C.A.M., Stefanescu, C., Lundsten, K.E., Maes, D., & Greatorex-Davies, J.N. (1998) Migration of the painted lady butterfly Cynthia cardui in Europe: evidence from monitoring. Diversity and Distributions, 4, 243-253.

Pollard, E. & Greatorex-Davies, J.N. (1998) Increased abundance of the red admiral butterfly Vanessa atalanta in Britain: the role of immigration, overwintering and breeding with the country. Ecology Letters, 1, 77-81.

Stefanescu, C. (2001) The nature of migration in the red admiral butterfly Vanessa atalanta: evidence from the population ecology in its southern range. Ecological Entomology, 26, 525-536.