Food, feeding rates and assimilation in the land snail Cepaea nemoralis L.

The natural diet of a population of Cepaea nemoralis living in a sand dune system in southwest England was investigated by field observations and examination of crop and faeces contents. The food consisted of dead material from the commoner plants on the site. Very little green matter was eaten and there was little evidence for seasonal variation in the diet.Consumption and egestion rates were measured gravimetrically on natural foods (dead leaves of Taraxacum officinale and Ononis repens) and artificial foods. Consumption rates were temperature dependent over the measured range of 5-20°C and also varied with the food substrate, an artificial food (rat food pellets) being consumed at the highest rate. High variability in the results can probably be linked to the live weight and activity cycles of the snails.Assimilation was estimated as the difference between consumption and egestion, since a trial of the ash-ratio method proved unsuitable with this animal. Assimilation efficiency did not vary with temperature over the range studied, but was dependent on food substrate, the two artificial foods (rat food pellets and lettuce leaves) being assimilated more efficiently (71-73%) than natural foods (30-44%).Faeces produced from the digestive gland could be distinguished and were measured separately. The amount produced was very small compared to the gut faeces, but increased significantly when a relatively indigestible food was used.