FIELD OBSERVATIONS ON FEEDING OF THE LAND SNAIL HELIX ASPERSA MULLER

Feeding of the land snail Helix aspersa (Müller) was observedat monthlyintervals. Three natural populations in Galicia (NW-Spain)were studied. At two sites only a fewplants constituted thebulk of the diet and in spring the snails' diet had the highestdiversity(H'). In the third population feeding and distributionof Helix aspersa(Müller) were observed in a small plotwith permanent patches of Urtica dioica.Nearly one half offeeding snails fed upon Urtica dioica. Most of the other observationswereon Mentha suaveolens, Ranunculus repens and Gramineae. The diversityofthe snails' diet showed seasonal variation with the maximumin the autumn months.Comparison between the availability ofthe different plant species and their contribution to thesnails'diet showed that the snails did not eat at random; Urtica dioicawas eatenmuch more than expected from its occurrence and grasseswere strongly under-represented in thesnails' diet. Temporalchanges of availability were significantly correlated with theamountseaten in the case of Urtica, but not for the other food plants.The distribution ofthe snails in the plot was significantlycorrelated with that of Urtica. Chemical analysesof the foodplants revealed Urtica as the species with the higher protein,ash and calciumcontents. The strong preference of Helix aspersafor Urtica dioica could beexplained by the value of Urticaas food or by its suitability as habitat for the snails. Thelargestproportions of green material in the snails' diet occurred inthe spring and juvenilesate more green material than adultsin the three populations. (Received 16 March 1998; accepted 30 November 1998)