Snails

Molluscs of the class Gastropoda. Many species of gastropod exist, adapted to life in the sea, fresh water and on land. Land snail shells are frequently preserved in buried soils, the fills of ditches, and other deposits over limestone subsoils. They are not preserved in the wet and acid conditions which determine the survival of pollen. Conversely, pollen is not preserved in the well-drained, base-rich environment of the lowland limestones, and so land snails fill a considerable gap in environmental reconstruction. The main factor governing snail ecology is water loss. Snails have a variety of strategies for avoiding drying-out during the day. Some spend their lives in water, or in marshy areas; others, the ‘shade-loving’ species, live only under vegetation cover, often burrowing through the leaf litter on top of the soil. The ‘open-country’ snails have adapted to life away from dense cover, reducing their water loss by thicker shells, specialized behaviour or physiological mechanisms. In addition, there are ‘intermediate’ or ‘catholic’ species that live in a variety of habitats, shaded and open. These include many of the more common species of snail. Using these categories of snail ecology the relative frequencies of shell fragments from different species, extracted from deposits and soils, can be used to reconstruct ancient environments. Snails do not travel far, and can only be used to investigate local changes in vegetation cover, but the method has been used with success at a number of sites, notably Neolithic monuments on the chalklands of southern England.