AUTOTOMY IN ARIONID AND LIMACID SLUGS

The occurrence of autotomy was investigated in five terrestrial slug s pecies. Half of the Deroceras reticulatum and 80 per cent of the Limax tenellus slugs which were stimulated mechanically in the tail, autoto mized the tail. Arion fasciatus, Arion subfuscus and Limax cinereonige r did not show any signs of being able to autotomize. The autotomized tail of D. reticulatum and L. tenellus was small compared to the total body weight and also to the weight of many predaceous beetles. D. ret iculatum and L. tenellus escaped in a few seconds after the beginning of mechanical stimulation; the reaction time was significantly shorter than that used by species which did not autotomize their tail. Compar ison between A. fasciatus and D. reticulatum also showed that D. retic ulatum sought for refuges significantly more effectively than A. fasci atus. The exposure of D. reticulatum to the beetle Pterostichus niger indicated that autotomy can stop a beetle long enough to let the slug escape. It seems that autotomy has evolved more frequently in those sp ecies which rely to a great extent on escaping and hiding when defendi ng themselves, than in species whose physiology and/or environment do not enable them to hide quickly after an attack.