Noterus crassicornis (Müller, O.F., 1776)
The 'Smaller Noterus'
This widely distributed species is generally common throughout much of its continental range; native to the Palaearctic and the Near East, it occurs from France east through the Balkans, Turkey, Iran and Mongolia to China, and from Italy north to Southern Scandinavia and the U.K. Here it is a local and generally rather uncommon species with a patchy distribution through England, Wales and Ireland including Anglesey and the Isle of Wight, and there are a few records from Scotland. The typical habitat is still or slow-moving water bodies with plenty of vegetation and detritus; canals, drainage ditches, lake and pond margins etc. and while there are plenty of coastal records, more especially in the east of England, it does not, unlike the more common N. clavicornis, inhabit brackish water environments. Adults occur year-round, they overwinter out of the water among marginal litter and plant roots etc. and become active in early spring, the life-cycle is much the same as clavicornis, with oviposition on submerged leaves and stems in the spring, and the predaceous larvae developing among aquatic vegetation and substrate through the spring and summer, respiring by tapping into submerged plant tissue with the tip of the abdomen. Pupation occurs in a cocoon attached to aquatic roots or stems and new generation adults appear from mid-summer.
In general appearance this species resembles N. clavicornis but it is smaller and generally a darker red, including the ventral surface, and in the male the lateral margins of the head and pronotum, as well as the front and middle femora, are darkened, sometimes virtually black. The prosternal process lacks the longitudinal ridge present in clavicornis; in males it is flattened while in females it is smoothly convex. The elytral punctures form three or four usually quite well-defined longitudinal series, and the raised part of the metacoxae is finely and rather sparsely punctured. The antennae are dimorphic; in the male the fifth segment id dilated and much longer than the sixth.