The feeding habits of some European pulmonate land slugs and snails are described. Although commonly pests in gardens, only a few species are necessarily injurious to crops. Most feed on wild plants and often on dead parts of the plants. The majority are herbivores, but others include omnivores and carnivores: many are important in the breakdown of detritus.
The feeding apparatus consists of a buccal mass housing a radula, jaw, odontophore cartilage, radula sac and a complex of muscles which operate the buccal mass during feeding. Snails feed by circular movements of the radula and jaw which together bite off pieces of food. Both show wear and old teeth are periodicallv shed from the radula.
Slugs and snails usually feed at night or at dawn. The position of food in the gut was determined by dissecting snails collected in the field at 4-hourly intervals. The crop was usually full early In the day but emptier later on. In spring and summer most snails dissected had fed, but in winter others had no food in the gut. Faeces were produced from 1½ to 7 hours after feeding.
Food plants in gut contents and faeces can be identified by their detailed structure. Monacha cantiana and Hygromia striolata fed mainly on Urtica dioica and Anthriscus sylvestris: M. cartusiana mainly on dead grass. Proportions of food plants in the gut varied with time of year.
The literature suggests that snails may select their food. Some plants are rejected on taste: hard plant surfaces may also inhibit feeding. Different plant communities support differing proportions of palatable food plants. Disturbed ground yields many, and chalk grassland fewer, proven food plants. Slugs and snails are probably important in the decay of dead plant material. Plant fragments in snail faeces are further decomposed by other animals, fungi and micro-organisms.
(Presidential Address, delivered 22 February 1975)