Megasternum concinnum (Marsham, 1802)

Quoted by Joy simply as very common without regional qualification, there are records throughout the UK including Scilly, Anglesey, the western Scottish islands, Orkney and towards the northernmost part of the Shetland isles (Unst)(NBN), perhaps most interestingly there are no records from the IOW or Man, but this also applies to three of our most common Cercyon spp.; C.haemorrhoidalis, C.quisquillius and C.melanocephalus, all of which occupy the same kind of habitats, so this may simply reflect a lack of recording. This species is common and usually abundant throughout our Watford area among decaying vegetable matter in a wide variety of habitats; they occur in dung of all kinds and often in large numbers (larvae are known to occur in this habitat (Skidmore,1991)) eg in horse dung in Whippendell wood and in older, drier cattle dung on Common moor, among reed litter samples from Radlett road, among decaying grass cuttings on West Watford golf course and in large numbers from compost heaps in town centre gardens. We have not recorded them from the considerable number of extractions examined from healthy fungus samples taken throughout our area but they occur in well decayed and ammoniacal fungal fruiting bodies in the autumn; decaying terrestrial bracket fungi among Fagus roots along the Grand Union canal near the A412 were found to contain hundreds of adults. Adults are common through the winter deep within heaps of decaying pond clearance in Cassiobury park and at this same location we have recorded them at MV (July, 2006). They have also been recorded from carrion, leaf litter and moss, sap of deciduous trees and, probably accidentally, in the nests of various mammals and in company with ants. Also from seashore drift (Hansen).

This small, shiny black and very convex species may be mistaken for the slightly smaller black mites often found in the same habitats, or in the same samples, with a little experience the beetles become obvious.

1.5-2.0mm (Joy) Very convex above and below, upper surface glabrous and shining, black to reddish brown, head usually darker in reddish specimens. Head transverse, broadest at eyes which are convex and continuous with outline, front margin straight or slightly sinuate, temples contracted towards base. Surface with fine and quite dense puncturation. Palps testaceous, as long as antennae, basal segment dilated. Antennae testaceous or darker towards apex, first segment (scape) constricted at centre, club elongate and truncate at apex. Pronotum broadest at base, evenly narrowed to right angled front angles, hind margin weakly sinuate behind obtuse hind angles. Puncturation fine, a little less dense than on head. Lateral margin lighter. Scutellum elongate. Elytra with well developed and complete, punctate striae, interstices flat and very finely punctate, surface shining but often with obscure and fine microsculpture, especially around scutellum and towards apex. Legs testaceous, all tibiae broad with small spines along outer edge. Meso and metatibiae with two stronger spines inside at apex. Pro-tibiae strongly emarginate at apex; having identified this as an Hydrophilid by examining the palps and antennae, the protibial emargination will identify this species. Tarsi 5-5-5, basal segment of metatarsi at least as long as second.

Description taken from 6 Watford specimens at X40

Skidmore, P. Insects of the British cow dung community. 1991. Field Studies Council.

Right Fore tibia

Constricted 1st segment of antennae