Behavioural responses by slugs to chemicalsfrom a generalist predator

Antipredator behaviour is not expected to evolve in response to generalist predators unless the prey forms a substantial proportion of the total diet of the predator and this predation is a major mortality factor. Since the generalist predator Pterostichus melanarius (Coleoptera: Carabidae) can affect the temporal and spatial dynamics of slugs, we investigated whether the slug Deroceras reticulatum responds to chemical cues from these beetles. We recorded the movements of slugs in arenas incorporating both a zone containing paper upon which the predatory beetles had been maintained and a control zone. Significantly more slugs accumulated on the control half of arenas after 24 h, with small slugs being quickest to respond. Slugs avoided paper exposed to both male and female beetles. They did not respond to paper that had been exposed to beetles and then stored for 5 days before the test. Slugs moved faster, turned less, spent proportionately more time moving and spent less time overall on paper exposed to male beetles than on control paper. This is consistent with a kinesis that would enable the slugs to escape rapidly from areas where predators were present. We conclude that slugs have evolved behavioural responses to chemical cues from either this generalist carabid predator in particular, or carabid beetles generally, many species of which include molluscs in their diets.