A generally common species throughout the central counties of Southern England but elsewhere very local and scattered; there appear to be no Welsh or Irish records and only very few from Southern Scotland. Further afield it is common throughout much of the Palaearctic east to Northern India. In the U.K. the adults appear in April or May and are common by late May or early June, remaining so throughout the summer. They occur in a wide range of wetland and permanently damp habitats; pond and river margins, parkland, woodland and gardens etc. being usually abundant where found. Typical host plants are various mints (Mentha spp.) on which both the adults and larvae feed although other hosts have been recorded on the continent e.g. basil thyme (Clinopodium acinos) and lesser catmint (Clinopodium clinopodium), both of which are widespread in the U.K. Adults are long lived and may overwinter twice, generally among matted marginal vegetation or tussocks and may occasionally turn up in winter extraction samples. Eggs are laid in May and June and the larvae hatch in mid or late June, feed through the summer and overwintering, they become active again in April when they feed for a short period before entering the soil to pupate. The adults are fully winged but only rarely fly.
This large and brilliantly metallic species is distinct among the U.K. coleoptera; the only confusion might occur with the superficially similar C. coerulans (Scriba, 1791), a recent addition to the U.K. list, this species also feeds on mint but is distinctive in lacking the longitudinal suture on the frons seen in herbacea.
Shape long-oval, sometimes almost parallel-sided, and large; 6.5-10.5mm. The colour varies from brilliant green, often with coppery overtones, to blue, purple or red, often with the suture narrowly contrasting blue, and sometimes specimens look distinctly bicoloured with the head and pronotum darker than the elytra. The appendages are black but distinctly metallic throughout. The head is coarsely punctured anteriorly, smooth on the vertex and with a fine
longitudinal suture which may only be visible towards the frontoclypeal suture. Pronotum transverse; the shape varies from almost parallel to quite strongly narrowed anteriorly, the surface has a mix of randomly distributed fine and coarse punctures but towards the lateral margins they become much larger. The surface is smoothly continuous to the lateral margins; without grooves or fovea. Scutellum large and obvious; usually coloured as the pronotum but lacking punctures. Elytra smooth and glabrous although in places usually transversely rugose, with a mix of fine and coarse punctures which are random but tend to run in longitudinal rows on the disc. The epipleura are strongly deflexed from the middle towards the apex so that in side view they are not visible in the apical half to third.
Generally slightly smaller (6.2-9mm)
Usually distinctly metallic blue.
Head smooth, without longitudinal groove.