Description

Medium-sized beetles, 5-15mm The species are very distinctive among the Chrysomelids and fall into 2 distinct morphological groups, both of which are instantly recognizable as members of the subfamily; Macroplea and Neohaemonia lack the metallic dorsal surface and the expanded tarsal segments, and have the outer apical elytral angle produced into a distinct tooth.  All species have a characteristic broadly elongate shape with the head prognathous and having distinct temples. The dorsal surface is usually strongly microsculptured and metallic; most are bronze, green or coppery and many have longitudinal stripes of contrasting colour on the elytra although in some species of Plateumaris e.g. P. rustica (Kunze, 1818) the body is entirely metallic black. The majority are glabrous but a few species of Donacia, sometimes considered to constitute a separate genus, Donaciella Reitter, 1920, have fine and dense dorsal pubescence. The eyes are round, convex and entire, a character that will distinguish them from the Criocerinae Latreille, 1807 and the Sagrinae Leach, 1815 where they are emarginate on the anterior margin. The vertex is convex, sometimes only weakly so, and often bears a longitudinal impression, otherwise the head lacks well-defined sutures e.g. the X- or H-shaped anterior impression seen in many other chrysos. The antennae are 11-segmented with all but the second segment very elongate. The head is as wide as, or a little narrower than, the pronotum, and both are distinctly narrower than the elytra. The pronotum is quadrate to elongate and usually rather parallel-sided being at most broadened towards the anterior margin, and is often constricted about the middle. The anterior and posterior margins are strongly bordered, all the angles are distinct and the lateral margins lack distinct borders. The surface often has a longitudinal impression and the cuticle either side is variously convex; often widely domed. The anterior prosternal margin is wide and the pro-coxae are round, convex and closely approximated, the prosternal process being reduced to a narrow ridge; the meso-coxae are round, prominent and widely separated, the mesosternum has a deep central longitudinal impression and the meta-coxae are quadrate and widely separated, reaching to the elytral epipleura. The elytra are subparallel to about half way and then narrow to a rounded or truncate apex, in some species e.g. Donacia crassipes Fabricius, 1775 there is a distinct albeit small tooth on the sutural angle. The shoulders are well-developed and each elytron has 10 distinct and usually strongly punctured striae, the cuticle often being transversely wrinkled, sometimes strongly so. In some species there are distinct impressions, often from below the shoulder obliquely to the suture and sometimes transversely so across the middle. The legs are long and robust; in many the femora are very long and dilated, sometimes only towards the apex, and in some they bear one or more teeth on the ventral margin- a character that is often sexually dimorphic-the tibiae generally have a single spur on the inner apical angle although this is missing from the hind tibiae of some Donacia. Tarsal formula 5-5-5; the two basal segments are broad, the third broad and deeply lobed, the fourth is small and the fifth is long and curved. In Neohaemonia and Macroplea the segments are long and cylindrical, the last segment especially so. The claws are curved and lack a distinct basal tooth. All species are fully winged and fly readily. Twenty one species included in three genera occur in the U.K. and these characteristic of the group as a whole.