Dytiscus semisulcatus Müller, O.F., 1776
Black-bellied Diving Beetle
This is a widespread western Palaearctic species occurring throughout Europe from North Africa to Southern Scandinavia and east to Turkestan; in the U.K. it is locally common and our most widespread Dytiscus being found throughout the mainland and Ireland including all the islands. Typical habitats are stagnant ponds and slow moving clear water with plenty of marginal vegetation and they also occur peat cuttings and among marginal sphagnum. Adults have been recorded throughout the year; hibernating among aquatic substrates etc and appearing in early spring. Mating occurs year-round and some oviposition occurs in the spring but the majority of eggs are laid in the autumn with the larvae developing through the winter and the following spring, fully grown larvae being most abundant during April. The larvae are thought to feed exclusively on caddis fly larvae. The adults may occur in large numbers where found and they fly well, being attracted to light.
22-32mm. The dorsal habitus of this species soon becomes obvious; elongate-oval, rather parallel-sided and appearing less convex than other members of the genus, the dark underside and posterior pronotal margin are characteristic. Head black with the clypeus and a small mark on the frons pale, the antennae are pale and comparatively short. Head and pronotum finely punctured in the male; more coarsely so and distinctly microsculptured in the female. Pronotum and elytra black with pale lateral margins. Underside dark with the hypomeron and lateral margins of the epipleura pale. Male elytra with 3 well impressed longitudinal striae, otherwise finely punctured. Female elytra sulcate with 10 longitudinal furrows in the basal two-thirds; females with smooth elytra occur in North Africa. Metasternal ‘wings’ broad, metasternal process broadly rounded at the apices. Legs slender and dark, brown to black. Metatarsal claws equal.