Carpelimus obesus (Kiesenwetter, 1844)
This widespread and generally common species occurs across the northern Palaearctic region to the Himalayas and the far east of Russia, it is present throughout Europe, except for the far north, from Spain to Ukraine, it is also known from Egypt but is otherwise absent from North Africa, there are also records from further afield due to importations but those from Canada, where it was formerly thought to be established, were based on misidentifications. It was first discovered in the UK in 1948 and is now widespread though local across much of south and central England. Adults occur year-round and are usually associated with wetland marginal situations where they live under debris or litter and feed on algae, usually on heavy soils with plenty of vegetation; although on the continent they also occur on sandy riverbanks. In South Herts. we find them among damp reed litter, usually in small numbers and usually among much larger numbers of other members of the genus and so sampling requires taking numerous specimens for detailed examination. Adults may be found by exposing the soil beneath debris or leaf litter and pootering specimens as they run for cover, they also appear in pitfall traps and among flood refuse or extraction samples throughout the year, they fly well and may be swept in flight over marginal vegetation during the afternoon and evening, and they also come to light.
2.5-3.5mm. This is among the few species of this large and difficult genus that may be confidently identified without the need for dissection the form of the antennae, head and pronotum, coupled with the dark appendages are distinctive. Body entirely shiny black and densely punctured, head and pronotum with fine pale recumbent pubescence, elytra with more erect and slightly darker yellow pubescence. Head with large convex and coarsely-faceted eyes which occupy most of the lateral margin, and short, rounded temples that do not protrude and are at most only a quarter the length of the eyes when viewed from above, penultimate maxillary palpomere long and gradually widened to the apex, apical segment small and very narrow. Antennae filiform with all segments elongate; 1-7 at least 1.5X longer than wide, and 8-10 at least slightly elongate. Pronotum widest in front of the middle where the lateral margin is roundly-angled, and narrowed in more or less straight lines to distinct obtuse anterior and posterior angles, surface finely and evenly punctured across the disc but more strongly and densely towards the lateral margins, disc with a variable but usually obvious longitudinal impression either side and there is a variable but smaller impression towards the basal half of the lateral margin. Elytra quadrate, with rounded shoulders and apical angles and only slightly wider towards the apex, without striae and evenly punctured throughout except for the basal area which is often wrinkled. Abdomen finely punctured and with very fine, wrinkled microsculpture. Legs substantially dark, sometimes entirely dark brown or black, but usually with the tibiae and tarsi to some extent pale creamy or yellow. Femora simple, tibiae without external teeth or spines and simply rounded apically, tarsi 3-segmented.