Bisnius fimetarius (Gravenhorst, 1802)

Joy quotes this species simply as common (which without regional qualification implies a national distribution) while the NBN map (May 2009) shows a very wide national distribution of post 1990 records north to Inverness including Anglesey as the only colonised island. Generallly common in our Watford area, the adults become abundant in late summer and autumn in suitable habitats. The species breeds in dung of all kinds and both adults and larvae are predatory (Skidmore). We have recorded adults from June through to the autumn on open dung pasture (etc) throughout our area although, up to May 2009, we have yet to find them in samples of horse dung from the bridle path in Whippendell wood. During warm weather the adults move rapidly and fly readily; when disturbed they are likely to crawl under or into a dry sample or to take flight so making sampling difficult although sweeping randomly among the many insects flying above such habitats will usually produce them. By far the largest numbers of adults recorded locally have been from large, rotting, wet and ammoniacal fruiting bodies of terrestial bracket fungi (mostly growing on the underground remains of dead Fagus roots) below Cassiobury park during the autumn; in 2007 and 2008 these often produced hundreds of specimens when sieved over a sheet at night.

Without extensive experience these medium sized dark staphs will need to be brought back and examined under the microscope, for a confident identification a few males should be dissected to provide reference material. The present species will become obvious with a little experience.

4.5-7mm (Joy). Head and pronotum shining black with very fine microsculpture (this mostly appears transverse and wavy and is obvious at X50), without any coloured metallic reflection. Head quadrate; in a series some appear a little elongate, temples rounded to base. Eyes small; shorter than temples. With four frontal punctures in a transverse series between eyes, central widely separted so that the four form two pairs, one inside each eye, between these pairs the vertex is depressed. Antennae black, inserted on the front of a transverse ridge above front margin of eyes, insertions lie inside outer margins of mandibles. With short and dense pubescence from fourth segment, segments 8-10 quadrate. Palps brown, terminal segment long and pointed. Pronotum elongate (23:19) and parallel sided with a series of four well impressed setiferous punctures in a longitudinal series either side of middle (may occasionally be an extra one on one side), between these and the side margin there are 3 or 4 similar sized punctures in anterior third. Lateral margin finely bordered and sinuate (side view). Scutellum black, as pronotum so contrasting against elytra, punctate and pubescent. Elytra shiny black with a bronze or green reflection, strongly and moderately densely punctured and with dense, backwardly directed, pale pubescence. Inner row of pubescence overlaps suture. Wider than pronotum, with prominent shoulders and dilated towards apex. Abdomen black or with very faint metallic reflection, strongly bordered, impressed transverse line at base of segments 1 and 2 straight. Finely punctate and pubescent as elytra. Legs pale brown, variously darker; in most specimens the tibiae and tarsi are darker than the femora. Tarsi 5-5-5. First segment of metatarsi shorter than segments 2-4 combined or fifth. Claws well developed but shorter than fifth segment.
Aedeagus characteristic; medially constricted, base wider than apex, base and apex smoothly rounded.

Description from 18 Watford specimens at X20,X50




Hind Tarsus

Aedeagus

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