Donacia semicuprea Panzer, 1796
A widespread species throughout England north to south Yorkshire and with a single record further north from the middlesborough area, in the southwest only two records west of Taunton, both from southwest Cornwall and a few from south Wales, mostly coastal (Cox, 2007). Found throughout the Watford area and by far the most common Donaciine species, they occur wherever the foodplant, Sweetgrass (Glyceria maxinia), grows and this is an abundant wetland species locally. Adults are conspicuous and easily recorded; usually occuring in large colonies and active in sunshine when they will fly readily when disturbed. In dull weather they may be found in leaf axils or low down on the stems, usually in pairs or small groups and usually facing downwards. Searching for the adult feeding signs will often reveal them as damage is usually extensive, a transparent membrane remains after they have consumed the upper epidermis and mesophyll. In most years the species is abundant but in some, only very occasionally in our experience, they appear to be more or less absent e.g. through 2007. Locally we record adults from April or May to October depending on season. Further afield they are likewise abundant along the Colne valley south to Cowley.

Eggs are laid in batches of 20-30 below the water's surface on Sweetgrass from May to August. Larvae are aquatic and have been recorded at the roots of Sweetgrass (Stainforth, 1944) from june and within cocoons in September, pupae have been observed within cocoons during September and November. Adults hibernate and have been recorded in cocoons in September and early November (Stainforth). The complete lifecycle takes three years (Bienkowski, 1996)

The longitudinal pronotal groove is unique to D.semicuprea and will serve to identify the species in the field.

6-9mm. Upper surface metallic bronze with green overtones, sides of elytra usually appear green when viewed in strong light from above. Head and scutellum with fine grey pubescence, pronotum and elytra glabrous. Head densely punctate, sometimes a little more sparsely so on vertex, with a usually well-defined longitudinal impression between eyes. Eyes convex. Antennae usually dark. Pronotum quadrate, surface uneven and coarsely punctate, punctures generally not confluent and cuticle smooth and shining. With a central longitudinal impression which is generally deepened anteriorly but always deeply foveate basally. Elytra with prominent shoulders, weakly rounded basally and broadest near middle, obliquely truncate at apex. Punctures of striae narrower than interstices which are shagreened and transversely strigose. Elytral suture simple. Legs dark and generally metallic, base of femora reddish-brown and tibiae lighter at base, meso and metatibiae often extensively so. Hind femora without teeth.

Description from 4 Watford specimens at X10

Stainforth, T. 1944. Reed beetles of the genus Donacia and its allies in Yorkshire. The Naturalist, 810:81-91: 811:127-139.
Bienkowski, A.). 1996. Life cycles of Donaciinae. In Chrysomelidae Biology 3:155-171. General studies. Amsterdam:SPB Academic publishing.

Sweetgrass beds, Cassiobury park