Paederus caligatus Erichson, 1840
This is a mostly western and central European species; it is very local and patchy in distribution, extending from Portugal to Bulgaria and Romania in the south, although it is absent from some of the Balkan countries, and north to the UK and Poland and it has also been recorded from North Africa and southwest Russia. Here it is very local and rare and the majority of records are from South Hampshire, it is otherwise widespread and sporadic; there are a few widely scattered records from West Sussex, Dorset, Carmarthenshire, Anglesey and Lancashire and it is also recorded from the east of Ireland. Habitats include a wide range of wet or permanently damp situations, typically open and exposed to the sun and usually with dense vegetation, fens and wet meadows etc, we have found them among a dense growth of iris beside a very muddy cattle pond in the New Forest and under wet blocks of peat on the Somerset levels and in both cases they were common. Adults occur year-round, they overwinter among tussocks and litter in drier situations and migrate back to wetlands early in the year, mating occurs over a long season during spring and early summer and they remain active into the autumn. The life-cycle has not been worked out but is very likely to be typical of the genus, with predatory larvae developing through the summer, passing through two instars and pupating in the soil to produce new-generation adults from July or August. Adults are diurnal and very active, they run rapidly on damp soil and climb plant stems in search of aphids etc, and they probably fly well, which is also typical of the genus, as the few specimens we have examined have been fully-winged. They are easily sampled by searching or pitfall trapping, although this last method can be very destructive in such habitats and should be used with caution, and they are usually distinctive in the field due to their extensively darkened legs.
6-7 mm. Easily recognized by the overall colour, more especially by extensively darkened legs which often have only the femoral bases orange; the only species that comes close to this is P. fuscipes Curtis, 1826; see below, head and abdominal apex black, elytra dark metallic blue or bluish-green, antennae dark with three or four basal segments orange. Head with weakly convex eyes and long temples that curve to a narrow neck, surface smooth and shiny with moderately large punctures around the margins, mandibles orange. Pronotum elongate, broadest in front of the middle and narrowed to a continuously-rounded apical margin and smoothly rounded posterior angles, surface with scattered long black setae. Elytra slightly elongate, slightly wider than, and measured along the suture, as long as the pronotum, moderately strongly and densely punctured and with long black setae throughout. Four basal abdominal tergites pale orange, strongly bordered and finely punctured throughout, apical segments without a distinct border, black and more finely punctured. Femora and tibiae long and slender, only the basal half of the femora distinctly pale, sometimes the tibiae are paler towards the apex but this is only gradual and never well-defined. Tarsi 5-segmented; basal segments of the front tarsi, and the fourth segment of the middle and hind tarsi bilobed. Sexes very similar but in the male the eighth sternite is narrowly and deeply excised.