Field observations on feeding of the land snail Helix aspersa Muller

Feeding of the land snail Helix aspersa (Muller) was observed at monthly in tervals. Three natural populations in Galicia (NW-Spain) were studied. At t wo sites only a few plants constituted the bulk of the diet and in spring t he snails' diet had the highest diversity (H'). In the third population fee ding and distribution of Helix aspersa (Muller) were observed in a small pl ot with permanent patches of Urtica dioica. Nearly one half of feeding snai ls fed upon Urtica dioica. Most of the other observations were on Mentha su aveolens, Ranunculus repens and Gramineae. The diversity of the snails' die t showed seasonal Variation with the maximum in the autumn months. Comparis on between the availability of the different plant species and their contri bution to the snails' diet showed that the snails did not eat at random; Ur tica dioica was eaten much more than expected from its occurrence and grass es were strongly under-represented in the snails' diet. Temporal changes of availability were significantly correlated with the amounts eaten in the c ase of Urtica, but not for the other food plants. The distribution of the s nails in the plot was significantly correlated with that of Urtica. Chemica l analyses of the food plants revealed Urtica as the species with the highe r protein, ash and calcium contents. The strong preference of Helix aspersa for Urtica dioica could be explained by the value of Urtica as food or by its suitability as habitat for the snails. The largest proportions of green material in the snails' diet occurred in the spring and juveniles ate more green material than adults in the three populations.