Philonthus marginatus (Muller, O.F., 1764)

A generally common species occurring throughout the British Isles (Chinery); both adults and larvae inhabit a variety of decaying animal and vegetable matter and are obligate carnivores, preying on other insects. Adults occur year round and are active from early spring until late autumn, during the winter they may be found in compost heaps etc and occasionally turn up in extractions. We have recorded adults from garden compost and from heaps of decaying grass cuttings on West Herts golf course, from beneath a dead rat along with other beetles, and from horse dung throughout our area eg during hot and sunny days they may be found in numbers within or beneath dung on the bridle paths of Whippendell wood, on such days the beetles often arrive in numbers, along with other species, within minutes of the dung being deposited. With the exception of sheep dung they have been recorded from all types of dung. When disturbed the beetles move rapidly and quickly vanish into soft substrate or into cracks in the ground etc or take flight. The broad yellow margins to the pronotum, which are unique and will readily identify the species, help to make the fast moving beetle cryptic and difficult to follow; the easiest way to observe them is to sieve a sample of substrate into a tray.

7-9mm (Joy). For the purpose of identification the colouration is unique among the Staphylininae; head and pronotum shiny black and usually with a weak metallic lustre, side margins of pronotum broadly and irregularly reddish yellow. Elytra widest behind middle, shiny to pitchy and dull due to dense puncturation and recumbent yellowish pubescence. Abdomen shiny black with faint bluish or bronze lustre. Legs vary from almost entirely yellow to extensively darkened. Antennae black with inside margin of basal segment yellow, without transverse segments. Eyes continuous with side margin of head, temples evenly rounded from behind eyes. Pronotum broadest at rounded hind angles and weakly narrowed to front angles, finely bordered. With four setiferous punctures in a longitudinal series either side of middle and several along the basal margin, two of which are in line with the longitudinal series.

Description from 6 Watford specimens at X10