LIFE FORMS AND HUNTING BEHAVIOR OF SOME CENTRAL-EUROPEAN STENUS SPECIES (COLEOPTERA, STAPHYLINIDAE)

Stenus species exhibit their greatest diversity in moist environments such as reeds. As seen in habitat choice experiments, they forage in t hree different zones: they are either (1) inhabitants of moist humus o r plant debris near the ground, (2) plant climbers or (3) surface runn ers on bare ground. A thorough comparison of 18 Stenus species has rev ealed different complexes of adaptations concerning predatory behaviou r and Linked morphological characters. Surface runners (3), such as S. comma, have laterally protruding eyes with a large number of ommatidi a, long legs and slender tarsi. Accordingly, standardized prey-capture experiments with springtails have revealed that these predators are h ighly agile and are capable of pursuing prey which move quickly and un predictably. Their searching behaviour is of the ambush-searching type . Moreover, they are less reliant on their specialized labium for prey -capture but have refined the mandible-attack mechanism. However, such life forms are an exception and may have evolved from (1) detriticolo us or (2) planticolous predator types that make up most recent Stenus species (e.g. S. pubescens). These beetles are not agile and stalk in plant debris or in the vegetation in order to hunt stationary or slow moving prey. Correspondingly, they have flat eyes, wide tarsi and depe nd to a higher degree on the labium, since it permits these predators, in spite of their limited agility, to catch prey in a sudden manner. (C) 1998 Elsevier Science B.V.