Differences in shell thickness in adult Helix pomatia L. from a number of localities in Southern England.

Large differences were found in the thickness of shells of Helix pomatia L. from different localities in Southern England. Snails from two populations showing such differences were raised from the egg stage under controlled conditions in the laboratory. Significant differences in shell thickness occurred and this suggests that those observed in the field are, at least in part, genetic. The ecological significance of shell thickness is discussed. Thicker shells were found to be associated with areas of low rainfall where breeding success is likely to be poor. It is suggested that thicker shells may result in longer life of individuals and enable them to survive a series of poor breeding seasons.