Leptacinus pusillus (Stephens, 1833)
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POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
XANTHOLININI Erichson, 1839
Leptacinus Erichson, 1839
This species is locally common and often abundant throughout the Palaearctic region from Portugal to the far east of Russia, it is common throughout Asia Minor and extends across North Africa to the Canary Islands and the Azores; in Europe it occurs to low mountain altitudes although extends to the subalpine zone in association with high mountain farms. To the north it extends far beyond the Arctic Circle in Russia and Fennoscandia but in the UK it is generally common across southeast and central England and very local and generally scarce further north to the Scottish Highlands and through Wales and mostly absent from the West Country. Further afield it has become established in many areas following introductions e.g. Australia and Tropical Africa, and it is one of three European members of the genuses – all of which occur in the UK - to have become established in the United States during the 19th century and are now widespread. Adults are present year round; they sometimes appear among flood refuse and in extraction samples of decaying vegetation through the winter and quickly become common from early spring and remain so into the summer. Typical habitats are dung pasture and stored decaying dung and straw mixture, here they may occur in large numbers and usually among several superficially similar species, they fly readily and are quick to colonize fresh horse and cattle dung; disturbing freshly crusted dung will often attract them in numbers, especially in hot sunny weather when they are easily observed in flight above the pasture, they otherwise appear among decaying vegetation and terrestrial bracket fungi in a wide range of habitats including woodland and moorland and especially on disturbed areas that are seasonally grazed by introduced cattle. Both adults and larvae are predators of other small insects and springtails etc, but especially diptera larvae which are usually abundant in the same habitats, larvae develop rapidly through the spring and early summer to produce large early summer populations of adults. Adults may be sampled from dung or netted in flight in warm weather; they also fly on warm evenings and are common in suitably placed light traps and flight-interception traps.
4.0-4.5 mm. Elongate and rather parallel-sided, with a relatively large head and distinct neck, body entirely dark; head black, pronotum and abdomen black or dark brown, elytra dark brown but sometimes paler towards the apex or yellowish inside the posterior angles, appendages pale brown but sometimes the basal antennal segment is darkened, head and pronotum with strong transverse and wavy microsculpture. Head elongate and distinctly narrowed from widely-rounded posterior angles to weakly convex eyes, temples about twice as long as the eyes and basal margin almost straight in front of a narrow neck, surface with scattered strong punctures and four frontal furrows; the outer pair extending obliquely from the front of the eyes onto the vertex, the inner pair shorter and almost parallel. Maxillary palps pale brown but usually to some extent darkened, penultimate segment broadened to the apex, terminal segment long and very narrow. Basal antennomere long and broad, segments two and three quadrate or nearly so and four to ten transverse. Pronotum elongate and broadened from rounded posterior angles to a curved anterior margin, with a longitudinal series of seven to nine punctures (rarely ten) either side of the disc and scattered punctured towards the lateral margins. Scutellum large and triangular, with a few scattered fine punctures. Elytra at most only slightly wider than the pronotum, with sloping shoulders oblique basal margins, usually almost parallel-sided but sometimes broadened towards the apex, strongly overlapping at the suture and with moderately strong punctures that tend to run in longitudinal series. Abdomen slightly broadened about the middle, strongly bordered laterally and with sparse fine punctures and fine transverse microsculpture throughout. Legs long and robust, especially the middle and hind femora, tibiae finely pubescent but lacking marginal spines, middle and hind tibiae with a strong terminal spur. Tarsi 5-segmented and simple. Distinguished among our UK members of the subfamily by its small size, the shape of the head along with the four frontal furrows, the number of punctures in the discal series and the extensively dark elytral colour.