Taking up calcium contained in the shells of dead snails or bird eggs is a common phenomenon in land snails. However, calcium deficiency can lead to uptake of calcium contained also in shells of live snails. At several sites we have observed Cepaea nemoralis gnawing at shells of live Helix pomatia and other Cepaea nemoralis. Sometimes the intensity of this behaviour was such that shells of virtually all live snails in a population, irrespective of their age, were damaged and in some cases holes through the shells could be seen. Those populations lived on acid (pH 3.6–5.9) and calcium-deficient soils (calcium content 96–774 mg/kg). Acid precipitation is recognised as one of the most important threats to terrestrial gastropods. Presently, with growing acidification of the environment, shell predation and cannibalism can be expected to occur more and more often and pose an additional threat to snail populations.