FORAGING BEHAVIOUR OF TERRESTRIAL GASTROPODS: INTEGRATING FIELD AND LABORATORY STUDIES

The foraging range of adult snails, Helix aspersa, has beenstudied using radio-transmitters. Snails did not return to anexact roost site after foraging, but often remained in the foodpatch, or returned only to the general roost area. Time lapse video films of the slug Deroceras reticulatum madeunder infra-red lighting in arenas were analysed for tracklengthsand degree of turning, in order to simulate slug movements inan unbounded situation. The results suggest that many food itemsare found by random encounter. Slugs usually ate the first food item found, but often ignoredfood items encountered later. If food was scarce, the slugsfed almost every time. Electronic recordings of bites on a wheatflour pellet over 24 hours show that feeding is most intensein the first two and a half hours from starting to feed, andlater meals are both shorter and less regular. Starved slugsdiffered from fed slugs principally by taking a second mealshortly after the first. When given a choice of a more preferredfood (maize pellets) and a less preferred food (pea pellets)in different ratios, the slugs appeared to encounter pelletsat random, but they fed more from the preferred pellets unlessthe ratio was 1 maize: 7 pea. Starved slugs ate twice as muchas fed ones.