Donacia vulgaris Zschach, 1788
This generally common species occurs throughout the western Palaearctic from North Africa to southern Scandinavia and from Portugal east through Asia to China to Japan, in the UK it is locally common through England and Wales, including the Isle of Wight and Anglesey but not, apparently, Man, and sparse and sporadic through Scotland including the Western Isles, and Ireland. The typical habitat is still and slow-moving water where the host plants, Phragmites (reeds) and Typha (rushes) occur. Adults occur year-round and are active from March until late in the year, generally into November, they are most common during late spring and early summer when mating pairs are commonly seen, and they are active in warm weather and take flight or drop to the water when disturbed, during cold spells or rain they tend to remain on stems low down near the water and are difficult to detect. Larvae develop within the roots and rhizomes of the host through the summer, obtaining oxygen from the host cells, and pupate in silken cocoons in the same situations from August. Adults eclose in late summer or autumn and remain in the cocoons through the winter, emerging from March onwards when they may be found in leaf axils. They are generally distinctive in the field; small and with a longitudinal stripe of metallic blue or red between elytral intervals 2 and 5 although this is sometimes missing.
5-10mm. Entirely metallic green or coppery, usually with a distinctive contrasting longitudinal stripe of colour between interstices 2 and 4 or 5. Head densely pubescent laterally; with a distinct median longitudinal groove and convex between this and a smaller groove beside each eye. Eyes large, coarsely-faceted and convex, antennae entirely dark or with the base of some segments obscurely lighter. Pronotum densely and often confluently punctured, the cuticle dull from fine microsculpture and with at most an indistinct median groove in the basal half (c.f. semicuprea), anterior margin with a tiny median projection. Scutellum triangular, very finely punctured and pubescent. Elytra more-or-less parallel in the basal half and then evenly curved to a weakly emarginate apex, punctures round and deep and separated by transversely rugose ground sculpture. Legs dark metallic with dense fine pubescence, especially on the femora and tarsi, pro-tibiae at least partly red, sometimes extensively so, and the meso- and meta-tibiae sometimes pale towards the base. Meta-femora not toothed ventrally and the meta-tibiae smooth internally. The combination of emarginate elytral apices, colour, pronotal features and partly pale legs are characteristic of this species.