Kateretes pusillus (Thunberg, 1794)
This widespread Holarctic species is locally common throughout Eurasia, extending above the Arctic Circle in Scandinavia, and across North America and Canada, in the UK it is generally common or abundant throughout England and Wales north to southwest Scotland although generally absent from the West Country. Typical habitats include all types of wetland e.g. marshes, river and pond margins, sphagnum bogs and floodplains etc. wherever the host plants, various rushes (Juncus spp.) and sedges (Carex spp.) occur, and they are often particularly common along damp woodland margins. Adults appear on the hosts during the first warm days of spring and are soon abundant, at this time they may appear in large aggregations feeding upon pollen and other flower parts but by May they are dispersing and may be found on a wide range of flowers e.g. umbels, nettles and grasses etc. usually near to but not restricted to wetland situations. They remain common until mid or late July and later may occur in extraction samples of wetland leaf-litter etc. Larvae develop in the flowers of rushes and sedges and descend the stems when fully grown to pupate in the soil.
1.6-3.0mm colour varies widely from entirely testaceous to black with well-defined pale elytral macula, more generally testaceous with the elytral margins dark. Entire dorsal surface strongly and densely punctured and finely pubescent; the head, pronotum and scutellum microsculptured and contrasting with the shiny elytra. The form of the basal antennomeres will identify this species; basal segment elongate and dilated, more so in the male, second segment smaller but much larger than the third, and 9-11 form an abrupt and loose club. Head triangular with prominent eyes and mandibles, clypeus with a weak transverse impression behind the antennal insertions. Pronotum transverse and widest towards the base, bordered and finely crenulate laterally, anterior margin rounded and without a border, posterior margin finely bordered, posterior angles widely rounded. Elytra quadrate or slightly elongate, smoothly rounded laterally and truncate apically leaving two abdominal sterna exposed. First visible abdominal sternite produced posteriorly at hind angles. Appendages pale; tibiae gradually widened to obliquely-truncate apex, each with two small spines at the inner apical angle. Tarsi 5-segmented with 1-3 bilobed, 4 very small and 5 elongate, claws smooth and without a basal tooth.
Male basal antennal segment only weakly expanded internally, second segment distinctly triangular.
Female basal antennal segment parallel-sided, second segment unmodified.