Paederus fuscipes Curtis, 1826
Among the most widespread members of the genus, this species occurs throughout the southern Palaearctic region and extends south into the Oriental and Australasian regions, it is generally common and frequently abundant in warmer southern areas but becomes more local and sporadic further north; it is common across south and central Europe and extends sporadically north into the UK and southern provinces of Fennoscandia. In the UK it is very local across the south of England and Wales, including the Isle of Wight and Anglesey; it occurs in the Lake District but is otherwise absent from northern England. Here it occurs in wetlands and permanently wet situations, including saltmarshes, and adults are usually common where they occur, typical habitats are marshy heathland areas, fens, and well-vegetated pond and river margins but we have also found them among sedges in peat bogs in Somerset and among sphagnum in South Hampshire. Adults occur year-round, they overwinter away from water and are active over a long season from February or March until late into the autumn, they are mostly diurnal but tend to remain among dense vegetation and are only rarely seen running in the open and so will need to be searched for carefully. Breeding occurs in spring and early summer; mating begins early in the season after a period of feeding, and females oviposit from late April until June, they lay eggs singly or in small groups into crevices in damp soil and larvae emerge between one and three weeks later, depending on temperature. In the UK they are univoltine but in warmer areas there may be two or more generations each year. Larvae develop quickly, passing through only two instars and becoming fully-grown within six to eight weeks, pupation occurs in a chamber below the soil surface and adults emerge after a week or so. Both larvae and adults are active surface hunters and take a wide range of prey including springtails and other insects, mites and soil nematodes but they are also known to consume decaying vegetable matter and adults commonly climb stems where they predate aphids and other insects. Adults fly well, they often do so in numbers
on warm evenings and are strongly attracted to light. Sampling is easiest by searching among marginal vegetation but they may be swept and both pitfall and light traps can be productive, but they will need to be examined carefully as several Paederus species may occur together – we once found all four UK species beside a pond in the New Forest – and they are closely similar. Further afield this is perhaps the most studied of the numerous members of the genus. It is among the most abundant and important predators of pests among wetland crops in eastern and south-east Asia, but is also the most common and serious cause of skin lesions and dermatitis in many countries from Iran to India and Japan and south through Malaysia and Indonesia, this is because there are several generations each year and huge populations build up which migrate between cropped areas and natural vegetation during harvesting, and when these mass migrations occur large swarms are often attracted by lights to towns and cities and beetles may enter shops, dwelling and high-rise apartments in , they may also cause serious problems among people working in fields as eggs, larvae and pupae may also cause serious skin problems when inadvertently crushed. People vary in their sensitivity to the beetles and in many areas seasonal precautions are taken but there have been some notorious outbreaks and they continue to occur, e.g. between June and September 1966 about two thousand serious cases were reported among US servicemen in Okinawa and a similar number of mild cases were also reported.
6-7 mm. Head black with a metallic reflection, pronotum and basal abdominal segments pale orange, elytra metallic blue, terminal abdominal segments black, legs orange with the femoral bases variably darkened, the hind tibiae are darkened in the basal third and often more extensively so, and the tarsi are usually darkened apically, the mandibles are yellow and the antennae are dark with two to four pale basal segments. Head with large, convex eyes and long, curved temples, surface shiny and unpunctured medially but strongly punctured laterally and across the base, penultimate maxillary palpomere broadly expanded and darkened toward the apex, the terminal segment much reduced. Antennae inserted laterally outside the base of the mandibles, 11-segmented and filiform. Pronotum elongate, parallel-sided and smoothly rounded anteriorly, posterior angles rounded and basal margin weakly curved, surface evenly convex and scattered setiferous punctures towards the margins. Elytra much wider than the pronotum, elongate, along the suture 1.1-1.25X longer than the pronotum, with rounded shoulders, slightly curved laterally and continuous and recurved across the apex, surface strongly and discretely punctured and finely pubescent throughout. Abdominal segments 1-4 strongly bordered and with scattered long, black setae, segments 5 and 6 not bordered and finely punctured and pubescent throughout. Legs long and slender; femora not toothed and tibiae without obvious spurs, segments 1-4 of front tarsi and segment 4 of the middle and hind tarsi strongly bilobed. Male with a long and parallel excision to the eighth sternite. [Aedeagus very small, about 1 mm, and very asymmetrical; in ventral aspect the right paramere smaller and differently shaped than the left-a feature unique among our UK species.]