FIELD OBSERVATIONS ON FEEDING OF THE LAND SNAIL HELIX ASPERSA MÜLLER

Abstract

Feeding of the land snail Helix aspersa (Muller) was observed at monthly intervals. Three natural populations in Galicia (NW-Spain) were studied. At two sites only a few plants constituted the bulk of the diet and in spring the snails’ diet had the highest diversity (H9). In the third population feeding and distribution of Helix aspersa (Muller) were observed in a small plot with permanent patches of Urtica dioica. Nearly one half of feeding snails fed upon Urtica dioica. Most of the other observations were on Mentha suaveolens, Ranunculus repens and Gramineae. The diversity of the snails’ diet showed seasonal variation with the maximum in the autumn months. Comparison between the availability of the different plant species and their contribution to the snails’ diet showed that the snails did not eat at random; Urtica dioica was eaten much more than expected from its occurrence and grasses were strongly under-represented in the snails’ diet. Temporal changes of availability were significantly correlated with the amounts eaten in the case of Urtica, but not for the other food plants. The distribution of the snails in the plot was significantly correlated with that of Urtica. Chemical analyses of the food plants revealed Urtica as the species with the higher 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.