Chlaenius tristis (Schaller, 1783)
This is a widespread Palaearctic species which occurs very locally from France eastward to Siberia and China and north to the south of Norway and Sweden; it remains locally common in some southern regions but is generally rare throughout central and northern Europe where it has suffered a general and drastic decline over recent decades, having disappeared from many areas and now being red-listed almost everywhere. The nominate subspecies occurs throughout most of this range while ssp. reticulatus Motschulsky, 1844 occurs in eastern Russia and China. In the UK it is thought to have occurred at several sites in Huntingdon, Yorkshire and Cambridgeshire during the 19th century, based on records given by Fowler (1887), the last record was from around 1860 and it was for a long time considered to be extinct here until the discovery of a colony in north Wales in 1976 which seems to be stable, and there are also modern records from a few scattered locations in Ireland. The typical habitat is densely-vegetated wetland margins, often on sandy or calcareous substrates, and in southern Europe sometimes on the coast. Adults occur year round, they overwinter away from water; in Europe they have been found in coniferous woodland up to 2 km from wetland habitats, and return during the spring, they are are mostly nocturnal but are often active in warm weather when they run up and down stems and may enter the water. They are fully winged; they migrate by flight during spring and autumn and have been observed swarming during hot summer days in Southwest France. They fly both by day and night and are sometimes attracted to light traps in numbers. Breeding occurs in the spring and larvae develop through the spring and early summer in the same wetland habitats as the adults. At the Welsh site they occur on wet calcareous marshland and fen with patchy vegetation and exposed areas of peat, they are active from April until August and may often be seen running on the surface on warm sunny days.
Chlaenius tristis 1
Among the UK fauna this species is distinctive; medium sized, 11-13mm, and rather flat with the upper surface pubescent and punctured and with entirely dark antennae. Most specimens are dull black with a very weak metallic lustre and a much stronger green or blue lustre to the head. Some central European specimens may be weakly but distinctly metallic all over. The head is often wrinkled towards the base but otherwise lacks impressions, the temples are constricted behind very convex and protruding eyes and the surface is very finely punctured except for a single large setiferous puncture beside each eye. Mandibles robust, symmetrical and produced forward; not notched on the inner margin and lacking a setiferous puncture on the external face, terminal maxillary palpomere truncate and the third antennal segment glabrous, or at least much less pubescent than the fourth segment. Pronotum rounded laterally to obscure anterior angles and obtuse posterior angles, lateral margin almost straight or weakly sinuate towards the base and the basal margin sinuate, surface extensively punctured and wrinkled and usually with shallow and ill-defined basal fovea.. Elytra broadest behind the middle and evenly curved from rounded shoulders to a continuous apical margin, striae weakly impressed but obvious to the apex, interstices without dorsal punctures, with transverse microsculpture and pale pubescence. Epipleurs crossed before the apex. Fully winged. Fore-tibia with a well-developed antenna cleaning notch, and all tibiae with a single long apical spur. Male with the basal pro-tarsal segments dilated.