Oulema obscura (Stephens, 1831)
This is a widespread and generally common species throughout Europe, from France to Turkey and Ukraine in the south, north to Scandinavia and the UK and extending east through Siberia to China; here it is locally common across England and Wales becoming more scattered and local in Scotland. Adults occur year-round, they emerge from their overwintering quarters from early April to feed upon a wide range of monocotyledons prior to mating, recorded hosts include floating sweet-grass, Glyceria fruitans (L.), hairy brome, Bromus ramosus Huds, meadow fescue, Festuca pratense Huds, couch grass, Elymus repens (L.), perennial rye-grass, Lolium perenne L., Timothy grass, Phleum pratense L., swamp meadow-grass, Poa palustris L. etc. as well as a wide range of cereal crops including oats Avena spp., maize and corn Zea spp., barley, Hordeum sp., rye, Secale spp. and wheat, Triticum spp. although it rarely occurs on oats is not considered to be an important pest of any particular crop. Oviposition begins in May when eggs are laid singly or in pairs on host foliage, often in cavities eaten out by the female for the purpose, and larvae emerge after a week or so. Larvae feed on the outer leaf epidermis producing narrow elongate translucent strips, similar to the adult feeding signs, and are fully developed within 3 weeks; generally by late June although fully grown larvae have been recorded into August suggesting a prolonged egg-laying period. Pupation occurs in a cocoon constructed near the base of a leaf and this stage lasts for about 3 weeks and new-generation adults appear from late July or early August. Depending upon conditions the entire life-cycle may take up to 10 weeks and there is only a single generation each year, new-generation adults feed into the autumn until seeking overwintering quarters under bark or among litter and tussocks etc. and in mild periods they may become active in the winter. Typical habitats include almost anywhere the hosts are thriving e.g. grasslands, farmland, wasteland, road verges and wetlands including salt marshes and river estuaries etc. and they regularly appear in domestic gardens. Adults are readily sampled through the summer by sweeping the host plants although from July they disperse and may occur on a range of herbaceous and woody plants, and through the winter they will also occur among extraction samples etc.
Adults will need to be examined carefully in the field as the widespread and common Lema cyanella (Linnaeus, 1758) is superficially similar; in that species the transverse pronotal constriction is further from the base so producing a lateral constriction near the middle, in the present species it is near the base.
3.0-4.0mm. Body entirely shiny metallic blue, rarely greenish or very dark, almost black, appendages black or with a faint metallic reflection. Head transverse; with very convex and prominent eyes, a smoothly convex and sparsely punctured vertex, and long and robust antennae which are broadly similar to those of Lema. Pronotum deeply impressed and laterally constricted before the base, convex and shiny anterior to this and only sparsely punctured. Elytra with broadly rounded shoulders, near-parallel lateral margins and continuously rounded apically; all striae, including an abbreviated scutellary striole, consisting of large and deep punctures and so the interstices are narrower than those of Lema; in places only as wide as the striae. Legs long and robust, all tibiae with a pair of spurs at the inner apical angle and claws fused at the base.