THE IMPORTANCE OF MUCUS AS A DEFENSE AGAINST CARABID BEETLES BY THE SLUGS ARION-FASCIATUS AND DEROCERAS-RETICULATUM

The effect of mucus exudation on the survival of Arion fasciatus and D eroceras reticulatum was studied by exposing mechanically stimulated a nd control slugs to Carabidae beetles for 24 hours. A light stimulatio n, lasting three minutes, exhausted the copious flow of mucus for one day. A generalist, Pterostichus niger, significantly preferred stresse d D. reticulatum over control ones. Similarly, P. niger exclusively at e stressed individuals of A. fasciatus. Two beetles which specialize i n gastropods, Cychrus caraboides and Carabus violaceus, consumed an eq ual number of stressed and control D. reticulatum and A. fasciatus. Th e susceptibility of the slug species to predation was different: for e ach beetle species, the proportion of available D. reticulatum preyed upon was significantly higher than that of A. fasciatus. The differenc es in the behaviour of A. fasciatus and D. reticulatum in defending th emselves against attacks is described. The main reason why specialist beetles are able to hunt slugs successfully is their ability to preven t the slugs from exuding large amounts of mucus. This may succeed by d ifferent means: C. violaceus targeted their killing strokes against th e posterior part of the mantle while C. caraboides hit the head of the slug. In both case the strokes seemed to paralyze the slugs.