Cepaea is a genus of large air-breathing land snails, terrestrial pulmonate gastropod molluscs in the family Helicidae.

The two species in this genus, C. nemoralis and C. hortensis, are widespread and common in Western and Central Europe and have been introduced to North America.

However, molecular phylogenetic studies suggested that two of them should be placed in the genera Macularia and Caucasotachea, which are not immediate relatives of either Cepaea or each other:[3][4] The range of C. hortensis extends further north than that of C. nemoralis in Scotland and Scandinavia and it is the only one of the two species in Iceland.

However, they differ somewhat in their behaviour: C. hortensis is more active at lower temperatures, aestivates higher on the vegetation and is more diurnal, although this appears to be independent of whether the other species is present or not.

Darker shells heat up more quickly in the sun, which might well be advantageous for cold-blooded animals in shaded woodland but risks causing overheating and death in open habitats.

[11] Contrary to predictions, recent global warming has not led to a detectable increase in yellow morphs on a continental scale.

However, song thrushes (Turdus philomelos) break open Cepaea shells on stones ("anvils"), allowing a comparison of those they predate with those present in the local environment.

The two Cepaea species colonised much of Europe only within the last 4000 generations,[17] so the time available for selection to act has been limited, and local anthropogenetic disturbances must often have reversed which morphs are optimal.

[27][28][29] Nevertheless, occasional transfer of genes between areas of different habitat is proposed to be important in maintaining the local diversity of phenotypes.