Phalacrus fimetarius (Fabricius, 1775)
This very widespread Palaearctic species occurs throughout Europe north to Scandinavia and is locally common throughout much of its range. In the U.K. it is common, though local, across Southern England and Wales north to Suffolk and Leicester. Adults occur from April to October in a wide range of habitats, more especially so in calcareous or limestone regions; grassland, parkland, wooded borders and wasteland etc. where they may be swept from various low vegetation. During warm weather they may be found on flowers, and sometimes in numbers; ox-eye daisy (Leucanthemum vulgare) seems to be a favourite. The larvae develop on plants infected with smut fungus (Ustileginales), flowering grasses are favoured and chalk false-brome (Brachypodium pinnatum), a calcareous species that flowers between June and August, is thought to be the preferred host, they develop among the flower spikes consuming the fungus. The very convex form and entirely dark colouration make members of the genus distinctive in the field but at the specific level they will need to be examined under a microscope.
Although small at 2-3.5mm, larger specimens are among the largest of the U.K. phalacrids. Very convex, oval and entirely shiny black above; the underside is flat which is suggestive of certain hydrophilids or Coccinellids but experience will soon make the species obvious. The head is mostly hidden by the thorax, finely punctured and with slightly convex eyes that follow the contour of the lateral margin. Mandibles trifid. The antennae are inserted in a pit under the lateral margin in front of the eyes; segments 1 and 2 are large and 9-11 form an elongate club, the terminal segment is very long and diagnostic among the U.K. species. The pronotum is evenly rounded and very convex, the lateral margins strongly bordered and the basal margin weakly sinuate. Surface punctation finer than that on the head, microsculpture not obvious at X60. Scutellum large and broadly triangular. The elytra bear a single stria close to the suture and there may be traces of others, the punctation is very fine and random although it tends to form lines on the disc and laterally. The surface microsculpture is very fine and best seen at the base at X90. Legs black, short and broad with the tibiae, especially the middle pair, broadened towards the apex. Tarsi 5-5-5, the third segment strongly bilobed, the fourth tiny and the terminal segment long. The claws are appendiculate, smooth and strongly curved at the base. This species is most easily recognized by examination of the fine spurs on the outside margin of the front tibiae; these are present from the basal third and become more dense and a little longer towards the apex so that there is a ‘comb’ of a dozen or more, these must be viewed obliquely as they curve downward and so may not be obvious from above.