Ilybius ater (De Geer, 1774)
This is a generally common species occurring throughout Europe, including Scandinavia, and east to Russia and Ukraine. In the U.K. it is common and widespread in lowland areas north to the Scottish Highlands and is likely to be among the first species recorded when embarking upon a study of the group. The typical habitat is among aquatic vegetation by pond and lake margins and the adults are likely to be present in numbers when found. They often occur alongside other medium sized water beetles e.g. Agabus bipustulatus, Ilybius fuliginosus or Colymbetes fuscus. Beyond this they occur in a variety of situations including fens, drainage ditches, peaty pools and brackish water. Adults fly well, are attracted to light, sometimes far from water, and are quick to colonize new environments. They occur year round but are seldom found later than October and are most abundant during May and June. Oviposition begins in late summer and autumn and first instar larvae occur from august, second and third instar larvae have been recorded in December. Adults overwinter out of water among moss or leaf litter etc. and are among the latest water beetles to emerge in the spring. Freshly eclosed adults have been found in June and July.
12.5-15mm. Easily identified by the combination of large size and black colouration although some specimens have a weak bronze lustre. The overall form is very convex and the entire dorsal surface is distinctly microsculptured, more strongly so in the female so that the species has a satin appearance. The antennae and palps are clear rufous, the anterior margin of the clypeus, labrum and two spots on the vertex behind the eyes a darker red. Pronotum strongly transverse with protruding front angles and a straight or only weakly sinuate hind margin. The surface behind the front and hind margins is weakly and randomly punctured. Scutellum slightly transverse. Elytra with three rows of weak and random punctures which may be indistinct towards the base. Lateral margins and often a preapical spot red. Legs dark red. Basal segments of the pro- and mesotarsi in the male with dense, long sucker hairs below. Hind femur with a short series or ‘comb’ of spines on the under surface near the apex, easily seen from the side. Metatarsal segments lobed below, claws unequal; the anterior shorter than the posterior. Swimming hairs on the upper surface of the meso- and metatibiae obvious.