Cepaea nemoralis

Shell patterns due to the degree of banding and darker or lighter color in the common European land snail (Cepaea nemoralis) are determined genetically. Studies show that visual predators such as thrushes preferentially sight the less cryptic snails in any environment. This has been shown experimentally by examining the remains of snail shells at so-called "thrush anvils," large flat rocks on which the birds drop the snails to crack them and eat the contents. The four corners of the graph show the environments in which each combination is more cryptic: light banded snails in grassland (upper left), dark unbanded snails in dimly-lit woodlands (lower right), and so on.