Asaphidion curtum (Heyden, 1870)
Formerly confused with the closely similar A. flavipes (Linnaeus, 1760) and so the distribution is not yet well understood but A. curtum is certainly widespread and generally common species across western and central Europe, extending south to Italy, Algeria and Tunisia and north to Denmark, where it is very rare, and the UK. First recorded in the late 1920’s it has also become established in North America following introductions from Europe. It is represented in the Canary Islands by the subspecies delatorrei Uyttenboogaart, 1928. In the UK it is the most frequently recorded species; it is locally common throughout England and Wales north to Yorkshire and more local and scattered further north to the Scottish border, beyond this there are a few isolated records from around Inverness. Adults occur year-round, peaking in the spring and autumn, and occur in a wide range of habitats, often in damp and shaded habitats such as permanently damp woodland but also in marshes and marginal wetland habitats, but they are also frequent on arable land and in parks and domestic gardens, occurring under debris or beside pathways. They are primarily diurnal and tend to lead concealed lives although they may be observed on open ground during the warmest weather. They may be found by searching among litter, under debris or in Carex tussocks etc. but they are frequent in pitfall traps and may occur in extraction samples at any time of the year, they are fully-winged but very rarely sampled in flight. Breeding is thought to occur in the spring with larvae developing through the summer to produce new-generation adults that will overwinter.
3.8-4.5mm. Rather like tiny versions of Elaphrus, species of Asaphidion are very distinctive and should not be confused with any other genus; Forebody narrow, elytra elongate-oval, entire dorsal surface dull metallic silvery, greenish or coppery and finely pubescent. Head distinctly wider than the pronotum, with massive convex eyes that occupy almost the entire lateral margin, vertex slightly depressed along the middle, clypeus protruding in front of the eyes and inner margin of eyes with two variously complete fine ridges. Antennae pale
with distal segments gradually and only moderately darker, the terminal segment often pale. Maxillary palpi entirely pale. Pronotum transverse, curved anteriorly and sinuate across the base, lateral margin angled just in front of the middle and narrowed in almost straight lines to obtuse anterior angles and sinuate and protruding posterior angles. Surface confluently and rather strongly punctured, more densely so towards the base, lateral margins distinctly bordered and with a setiferous puncture inside the median angle and at the base of a fine ridge inside the posterior angle. Elytra long-oval, with rounded shoulders and a continuously rounded apical margin, surface without striae, finely punctured throughout and each with at least 2 well-defined setiferous fovea, there are usually with others that are less well defined or simply produce an uneven surface. Legs entirely pale or with the tarsi and, rarely, the knees infuscated.
Among our UK species curtum may be identified as follows. A. pallipes (Duftschmid, 1812) is always larger, at least 5mm, and lacks the keels inside the pronotal hind angles. A. stierlini (Heyden, 1880) and A. flavipes (Linnaeus, 1760) have the knees consistently darkened and the antennae rather abruptly brown or black from the fifth segment, contrasting strongly with the basal segments. A. curtum also differs from our other species in having the aedeagus constricted before the apex and produced into a short lobe.