can also be yellow, pink, chestnut through to dark brown, and the shells can be with or without dark bandings. The bands vary in intensity of colour, in width and in total number, from zero up to a total of six. The polymorphism has been intensely studied from 1940 onwards for its heredity, evolution and ecology. Researchers have variously asserted that the cause is random genetic drift, different natural selection pressures in different areas (the snail often has darker camouflage in woodland, lighter in rough grassland) with mixing by migration, and balanced polymorphism. Balanced polymorphism could arise when a predator like the song thrush has a given 'search image', so it tends to see and kill snails of a particular colour and pattern. Natural selection would then favour a diversity of colours and patterns as an antipredator adaptation. However it appears that no one explanation is the whole answer: most probably, the polymorphism has several causes, including selection of paler, more reflective colours in hot environments to reduce water loss. Different coloration and banding of the shells of Cepaea nemoralis: Distribution The native distribution of this species is from northern and western Europe to central Europe, including Ireland and Great Britain. The species is rare and scattered in northern Scotland, where it has been introduced. It is not found in the Hebrides, Orkney or Shetland. It seems to have been affected by air pollution and soil acidification in some parts of England. The species is found in France, Netherlands, Switzerland, Austria, Germany, eastwards to northwestern Poland, Czech Republic, SW Hungary, southern Portugal, central Spain, Bosnia, in Italy to Lucania, and as far north as southern Sweden. In Eastern Europe it is found in Latvia, Kaliningrad, Estonia (Hiiumaa island), and Ukraine. No doubt aided by human transport, this species is a good colonizer, and is often found in gardens, parks and abandoned land in cities. In Eastern Europe it occurs in urban areas. More recently, the grove snail has been introduced to North America, and Venezuela. It has been reported in British Columbia and Northern Ontario, Canada as well as in western Washington State. The white-lipped snail has a similar range, but that species extends further north, to border the Arctic. Biology and ecology This is a very common and widespread species in Western Europe, occupying a very wide range of habitats from dunes along the coastline, to woodlands with full