Agabus bipustulatus (Linnaeus, 1767)
This is a very widely distributed species and one of the most common water beetles throughout its European range; it occurs throughout Europe from North Africa to Iceland and east through Asia Minor to Siberia and China. Further south it occurs in tropical Africa. In the UK it is probably our most common medium sized diving beetle; it has been recorded throughout, including all the islands north to Orkney and Shetland. It may be found in almost any wetland habitat including peaty pools and brackish environments. The species prefers standing water but also occurs in sheltered and slow moving parts of rivers and among marginal aquatic vegetation. It is almost always present in numbers in fens, drainage ditches and stagnant detritus pools, cattle troughs and garden ponds etc. The adults are strong fliers and quick to colonize new environments; flooded tyre ruts in woodland areas in the spring often host considerable numbers. Wetland habitats that dry out in late summer are worth searching as the adults may be found under matted vegetation, under logs or among cracks in the soil. Adults sometimes come to light and often land on cars, attracted by the polarized light. The species has a long breeding season; both adults and larvae occur throughout the year and freshly emerged adults have been recorded from May to September. Both stages are predatory, feeding on a wide range of prey items. The larvae lack swimming hairs and move by walking, they leave the water and build a spherical earthen cocoon in which to pupate.
9.5-11.5mm Elongate oval and depressed but the shape varies, the outline may be continuous or it may be constricted between the pronotum and elytra. Usually black or with reddish elytra and often with a bronze lustre, especially in the male. Legs dark red. Antennae pale with the distal half of the terminal segment dark. Two spots on the vertex of the head and the posterior margins of the sternites red. The pronotal and elytral microsculpture is characteristic of the species; the cells are very elongate, up to 6x longer than wide, and are obvious with a hand lens in the field. The basal segments of the pro- and masotarsal segments are dilated, and the claws are unequal in the male. In general the male is shiny and the female, with much more extensive microsculpture, is dull.