Donacia simplex Fabricius, 1775
This very widespread and generally common Palaearctic species occurs from Portugal to Mongolia and eastern Siberia, it has also been listed from Japan but this may be based on misidentified specimens, in Europe it is a mainly lowland species, extending to about 700 m; it is common throughout the region and extends north to the UK and beyond the Arctic Circle in Scandinavia, it is present on most of the Mediterranean islands and widespread in North Africa but absent from the Atlantic islands. In the UK it is common across England and Wales though less so in the north, sporadic and very local in Scotland, including the Outer Hebrides, and local across central Ireland. Adults are active from March until September but may sometimes appear during the winter. Typical habitats are margins of ponds, reservoirs and streams etc. where they occur on various plants including Sweet-grass, Glyceria fluitans R. Br., Bullrush, Typha latifolia L., Common Reed, Phragmites australis (Cav.) and sedges, Carex L. but especially bur-reeds, Sparganium L., and usually where the vegetation is dense. Adults are diurnal and are easily observed as they feed on the upper surface of leaves, they mate on the leaves during spring and early summer and females oviposit on submerged stems and foliage. Larvae feed within roots and develop rapidly through the summer, they pupate within a cocoon on the outer surface of roots from August and adults eclose later in the summer; most will remain in situ to overwinter but specimens are occasionally recorded through the winter. Adults may be readily observed on foliage and they are easily swept but they fall or take flight when disturbed and so can be difficult to study, they will also need to be taken for examination as several other closely similar species are common in the same habitats and mixed colonies are common.
Donacia simplex 1
Donacia simplex 2
7.0-11.0 mm. Body glabrous, usually metallic copper or bronze but specimens with a red, blue or green reflection are not uncommon, legs finely pubescent and substantially dark metallic but variously red or orange, especially the base of the tibiae and tarsal segments; the anterior tibiae often entirely pale, antennae dark with the basal part of most segments pale. Head with convex and protruding eyes and long temples, evenly convex and densely punctured above, posterior margins of the eyes with fine grey pubescence, frons with a long median groove that diverges posteriorly towards the eyes, the cuticle between this and the lateral grooves convex, clypeus emarginate medially Pronotum widest at obtuse anterior angles and unevenly narrowed to a sub-basal constriction, anterior margin smoothly curved (examine carefully as the closely similar D. vulgaris Zschach, 1788 has a tiny median projection), surface very finely microsculptured, sometimes with a weak longitudinal depression but without elongate fovea, punctation dense and often confluent. Elytra with broad rounded shoulders and slightly dilated behind the middle, apical margin truncate; the outer angle simply rounded or only very slightly produced, surface obliquely depressed from behind the shoulders, striae, including a long scutellary striole, strongly punctured and mostly distinct, interstices densely cross-rugose and very finely punctured. Distinguished from species of Plateumaris by the form of the suture; here it is simply abutting or slightly diverging towards the apex while in Plateumaris each side is crossed or inverted in the apical quarter. Femora without ventral teeth, hind tibiae smooth ventrally, tarsi pseudotetramerous with the third segment deeply bilobed.