Plateumaris sericea (Linnaeus, 1761)
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POLYPHAGA Emery, 1886
CHRYSOMELOIDEA Latreille, 1802
Plateumaris Thomson, C.G., 1859
This species is generally common throughout the Palaearctic region from Europe through Asia Minor, Kazakhstan and Russia to Mongolia, China, Korea and Japan; it occurs throughout Europe from the Mediterranean to the far north of Fennoscandia and the UK and is often the most common member of the subfamily. Adults have been recorded throughout the year but are generally active from April until September, peaking in abundance from May until July, they occur in well-vegetated wetland marginal situations, usually beside still or slow-flowing neutral or basic waters beside ponds, river margins, marshes, gravel pits and drainage ditches etc. and are also recorded from reed beds and saline swamps and pools, ant they are almost always present in numbers. Host plants include various bur-reeds (Sparganium L.), especially branched bur-reed (S. erectum L.), bulrush (Typha L.), Yellow iris (Iris pseudacorus L.), and common club-rush (Schoenoplectus lacustris (L.) Palla), salt marsh club-rush (Bolboschoenus maritimus (L.) Palla) and various sedges (Carex L.) but adults fly well and may disperse widely on warm spring and summer days and so are may be found on a wide range of waterside plants and flowers including those of water-lily (Nuphar Sibth. & Sm.) buttercup (Ranunculus L.) and various umbels (Apiaceae Lindl.) Mating pairs a are common on marginal foliage and flowers from spring to early summer and females lay small batches of eggs on the underside of leaves, probably below the water and protected with a gelatinous secretion which is typical of the family, and larvae develop among the feed externally, developing among aquatic roots, they develop rapidly and adults have been found within cocoons on host roots during August and September, these will remain in situ until the following spring although specimens are occasionally recorded throughout the autumn and winter. Adults feed by scraping away the upper epidermis of leaves, they leave behind wide translucent strips of lower epidermis, usually parallel to the main vein, which may be extensive and include most of individual reed and rush leaves, this may be a good sign of their presence although this kind of feeding is common to the subfamily generally. Sweeping through marginal vegetation will usually produce adults in numbers.
6.5-10.0 mm. Very typical of the family, elongate with a narrow forebody and broadly-oval elytra, but notably variable in colour from metallic bronze, gold, red or green to vivid blue or violet, the appendages are dark but also substantially metallic, matching the body. Black individuals occur rarely on the continent. Head with convex and protruding eyes in front of short converging temples and a short, almost parallel-sided neck, surface densely punctured and rugose and with a deep median longitudinal impression, antennae elongate and slender, the fourth segment about twice longer than wide and distinctly longer than the third. Pronotum quadrate or nearly so, constricted before the base and with a large swelling before the anterior angles, surface rugose, impressed medially and equally and finely punctured throughout, without oblique wrinkles except sometimes along the basal margin. Elytra with broadly-rounded shoulders and a continuous apical margin, with strongly punctured striae which may fade among strong microsculpture about the apex and usually at least to some extent cross-strigose, often extensively so, surface widely depressed medially about one-third and two-thirds from the base, suture inverted towards the apex. Front and middle femora smooth below, hind femora with a strong ventral tooth. The sexes are very similar but females have broader and more parallel-sided elytra.