Contacyphon padi (Linnaeus, 1758)
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This is a common and often abundant species throughout Europe, extending east from Spain into Asia Minor and western Russia and north to the UK and far above the Arctic Circle in Fennoscandia; it is common throughout the UK and Ireland and occurs on all the islands north to Orkney. For many years it has been quoted as widespread in the Nearctic region but these records are now thought to be based on another species. Adults occur over a long season from April until September or October, they peak in abundance during March and again, in much larger numbers, during August, and are generally associated with wetlands and wetland margins; they can be very common in densely vegetated eutrophic still water habitats and are often abundant around peaty moorland ponds but more generally they are likely to be common in any densely vegetated marginal situation as well as in permanently damp situations e.g. among sedges on floodplains that dry out in the summer. They are diurnal and live mostly among foliage but during warm weather they occur on flowers, in the spring sometimes on hawthorn blossom, and often in large numbers where they may be observed feed on pollen, mating begins in the spring and continues into the summer. Little is known of the biology but larvae are aquatic and, typical of the family, microphagous, feeding on diatoms and algae which they filter from the water, and pupation occurs in marginal situations out of the water, new-generation adults occur from August and adults have been recorded among litter etc through the winter although it is not known whether the species overwinters entirely in this stage as other members of the genus are known to overwinter as larvae. Adults are easily sampled by sweeping vegetation but care must be taken when recording as they often occur along with numbers of other members of the genus.
At 2.0-2.5 mm this is among the smallest of the UK members of the genus and smaller specimens are almost certain to be this species. They are shiny and finely pubescent and variable but often recognizable in the field by the distinctive and rather dark colouration; head dark brown to black with the labrum pale brown, pronotum dark brown with pale lateral margins or, rarely entirely pale brown, elytra variable from entirely pale to dark brown but usually pale brown with the base, suture-the apex is usually pale- and lateral margins darkened, antennae extensively dark but with the second and third segments pale and the basal segment variable but darkened to some extent, legs pale with the femora and sometimes the penultimate tarsal segment dark. Ventral surface very dark brown to black, except for the elytral epipleura, and very finely punctured and pubescent. Head produced in front of large convex eyes, smoothly convex and finely punctured and with fine and rather long pale pubescence, antennae inserted laterally in front of the eyes; 11-segmented with the basal segment large and roundly expanded internally, the third segment clearly shorter than the third and the remaining segments elongate and clearly wider than the third. Pronotum very transverse, broadest across slightly obtuse posterior angles and narrowed to a weakly sinuate apical margin, basal margin strongly curved backwards and slightly sinuate inside the angles, surface finely punctures, about as strongly but usually a little less densely than the head, pubescence semi-recumbent, fine and directed backwards. Scutellum large triangular and punctured and pubescent as the pronotum. Elytra elongate, with rounded shoulders and curved laterally to a continuously curved apical margin, without striae or ridges, rather densely punctured throughout, these stronger than those on the pronotum, and with fine overlapping pubescence. Legs short and slender, tibiae almost parallel-sided and without obvious terminal spurs, tarsomeres short and not obviously lobed; the basal segment of the hind tarsi shorter than the following segments combined.