Chaetocnema subcoerulea (Kutschera, 1864)

Widespread though generally very local and, especially in northern regions, scarce, this lowland species occurs from the Pyrenees to Greece and north to the UK, Denmark and southern Sweden and Finland. To the east it extends through Asia Minor and Russia, where it reaches the Arctic Circle, into western and central Siberia. In the UK it is locally common across southern England from Kent to Surrey and Hampshire and there are scattered records from East Anglia and Devon and much older records from Northern England and, possibly, South Wales. Adult beetles are present year-round; they overwinter among grass tussocks and litter or in moss and are active over a long season from April until the autumn, peaking in abundance during May and June. Typical habitats are wetland margins, wet heath and moorland, fens and marshes, and they are sometimes common beside drainage ditches in open woodland of all kinds. The species is associated with various Juncaceae and Cyperaceae, often Jointed Rush (Juncus articulatus L.), Sharp Rush (J. acutus L.), Prickly Sedge (Carex muricata L.) and True Fox-Sedge (C. vulpina L.) among others. Adults are capable of flight and the species is thought to be exclusively univoltine in the UK. Mating occurs in the spring and gravid females are common by July, adults feed on host foliage and larvae are known to develop within host rhizomes but beyond this the biology is not known. Sweeping host foliage and flowers is the best way to find adults, they are active even in overcast conditions and they usually occur in numbers.

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1.7-2.3mm. Narrowly-oval and discontinuous in outline, body entirely unmetallic dark blue to green or black, antennae dark with one or two basal segments pale (at least beneath), legs dark with tibiae and tarsi at least partly paler. Head uniformly and finely punctured throughout, vertex convex and frons flat; without a medial longitudinal keel between the antennal insertions, frontal wide and flat. Pronotum transverse, broadest about the middle and narrowed to a curved anterior margin and slightly obtuse posterior angles, surface shagreened and finely punctured throughout (although distinctly more strongly so than on the head), basal surface evenly convex, without impressions. Elytra evenly curved from sloping shoulders to a continuously rounded (sometimes slightly accuminate in females) apical margin, surface for the most part confusedly punctured, especially about the base and towards the margins, and usually with distinct, though often small, humeral calli. Middle and hind tibiae with a distinct external tooth-a feature that will distinguish the genus among our leaf-beetle fauna.