Odeles marginata (Fabricius, 1798)
Widely referred to in the literature as Elodes or Helodes marginata, this is a mostly western and central European species, it is locally common from France to Austria and Poland and north into the UK and the south of Fennoscandia, it occurs throughout the UK north to Shetland, it is present on all the islands, except for the Outer Hebrides, but is rare and mostly coastal in Ireland. Adults are diurnal and occur over a short season from April until June or July, the typical habitat is among vegetation beside fast moving streams and rivers, especially in cool and shaded forest areas, in northern Europe usually by cold, fast-moving streams in mountain areas and in shaded lowland forests, adults usually occur on marginal vegetation or shrubs although they also visit flowers to feed on pollen. Larvae resemble elongate woodlice, they have long multi-segmented antennae and short robust legs and are adept at crawling over rocks and stones in fast-moving water as they filter small organism and plant detritus, they often carry a bubble of air on the tip of the abdomen which they periodically release and then slowly produce another, eventually they rise to the surface to replenish their air through the abdomen which has a enlarged spiracles in a respiratory chamber formed by the eighth and ninth terga and short anal gill tufts, they develop through the summer and very probably overwinter and pupate among marginal substrate in the spring although this is not well-understood and pupation may occur in the autumn. Adults usually occur in small numbers; they occasionally appear when sweeping marginal vegetation but they disperse by flight and sometimes occur far from suitable habitats.
4.5-5.3 mm. Elongate-oval and moderately convex, very finely punctured and pubescent throughout, distinctive among our fauna due to its colouration; head black, pronotum yellow with a broad median longitudinal black band that reaches the basal and apical margins, elytra pale to dark brown, legs pale with darkened femora, antennae dark with three basal segments and the base of the fourth variously yellow. Head with large convex eyes and short, strongly-converging temples, surface weakly convex to a deep frontoclypeal suture, clypeus smoothly curved anteriorly, antennae 11-segmented and filiform, the second segment small and globular, the third tiny and 4-11 slender and very long. Pronotum widely transverse, broadest across perpendicular posterior angles and smoothly rounded anteriorly, basal margin strongly bisinuate, surface evenly convex and without structure. Scutellum large, triangular and punctured as the pronotum. Elytra smoothly curved from rounded or slightly-angled shoulders to a continuous apical margin, without striae and finely and densely punctured throughout, the punctures a little stronger than those on the pronotum. Legs long and slender with all femora of similar width, tibiae straight and parallel-sided; the middle and hind tibiae with a fine but conspicuous spur on the inner apical angle. Tarsi 5-segmented, the basal segment long but shorter than the others combined, and the fourth segment strongly bilobed.