Avoidance responses of some indigenous and exotic freshwater pulmonate snails to leech predation in South Africa

The avoidance behaviour elicited from four species of freshwater pulmonate snails, Physa acuta and Aplexa marmorata (Physidae), Bulinus tropicus (Planorbidae) and Lymnaea natalensis (Lymnaeidae), following contact with a molluscivorous leech Hebbdella conifera (Glossiphoniidae), was examined experimentally. Although H. conifera showed no species preference for any of those species it attacked, the physids, both exotics, were killed less often than would be expected by chance. The indigenous species, B. tropicus and L natalensis, were more susceptible to leech attack than the introduced species. Size-preference trials using P. acuta showed decreased susceptibility to leech attack with an increase in snail size. These results are interpreted with reference to the mode of leech attack and to differences in snail morphology.