Oulema erichsoni (Suffrian, 1841)
This widespread Palaearctic species has been recorded from Spain across to China, Japan and Korea in the east and from northwest Africa to Scandinavia and the UK in the north although in the UK it is very local and scarce; there are modern records only from North Somerset and former colonies in coastal South Devon and coastal East Sussex seem to have disappeared. On the continent the host plants are various cereals and other grass species but in the UK it appears to be monophagous on Floating Sweet-grass, Glycera fluitans (L.). Adults have been recorded in January and February and from May to Jul; they typically occur on the host in sparsely-vegetated wet peat cuttings and on heaths but little is known of their life cycle in the UK; both adults and larvae feed on the outer epidermis of host leaves and larvae cover themselves with a defensive layer of excrement and debris, fully grown larvae occur in May and June, pupation occurs in a cocoon among the host foliage and new-generation adults appear from late June. Our only encounter with the species was from wet peat cuttings at Shapwick in Somerset during early June, 2014 when a specimen was swept from Ranunculus flowers.
Body entirely black; forebody with a weak metallic reflection contrasting with the deep-blue metallic elytra, appendages black with a faint metallic reflection, superficially similar to Lema cyanella but with the lateral pronotal margins more parallel-sided and the constriction close to the base. At 3.8-4.5mm it is generally larger than O. obscura, the pronotum is less curved laterally and is finely punctured towards the basal and lateral margins, the elytra are longer, at least 3.5X longer than wide, and the elytral striae are less strongly punctured; at most much narrower than the interstices.