Onthophilus striatus (Forster, 1771)
This widespread though generally very local and uncommon species occurs throughout Europe from the Mediterranean north to the UK and the south of Sweden and extends through Asia Minor and Russia into Ukraine and western Asia; in the UK it is locally common across Wales and the south of England and sporadic and generally rare further north to the Scottish border. Adults are present year-round; they are active over a long season from early in the year but may be found in suitable habitats through the winter. Adults occur among decaying matter of all kinds; they are often common in garden compost but may also be found in leaf-litter, fungi and dung of all kinds, they are mostly nocturnal but will become active on warm sunny days e.g. during the 1980s we often found them in numbers running on pathways around canine droppings on pathways in West London. Larvae develop among the host material and are thought to be exclusively predatory on diptera larvae and other small insects etc. while adults are known to predate the eggs of other insects but are primarily filter feeders; the mouthparts bearing modified setae that apparently filter particles from liquids before they are consumed. Adults have also been recorded from the burrows or a wide range of ground-nesting mammals including mole, rabbit and hare and on warm summer days may be found in numbers among the litter and soil inside the burrow entrance. Sieving suitable material is the easiest way to sample adults, although they can run fast and are best sieved into a deep tray, but they may occur in extraction samples throughout the year and placing bundles of litter in burrows over the winter may also be successful.
Adults are small, 2.0-2.5mm, broadly-oval and discontinuous in outline and entirely black or dark brown in colour, usually with the appendages a little paler, and when seen moving in bright sun they have a shiny metallic appearance. Among our histerid fauna they are readily distinguished by the sulcate pronotum and raised elytral interstices. Head transverse and finely punctured throughout, with weakly convex eyes only narrowly visible from above and short parallel temples, vertex and frons with various indistinct raised areas and the clypeus raised transversely between the antennal insertions and narrowed to a straight anterior margin. Mandibles robust; curved and strongly toothed internally. Antennae 11-segmented; scape long, curved and strongly widened towards the apex, second segment globose and much wider than the rest of the funiculus, club elongate and oval. Pronotum widely transverse, broadest about the middle and strongly narrowed to slightly produced anterior angles, anterior margin curved forward and basal margin sinuate and produced medially. Surface densely punctured throughout; the disc with four complete longitudinal ridges and a lateral ridge which is usually only developed in the basal half or two-thirds. Elytra transverse, broadest behind the shoulders and narrowed to truncate apical margins, striae strongly punctured to the apex, between the punctures with two longitudinal ridges, interstices sharply raised throughout. Legs long and slender, all tibiae weakly curved, middle and hind tibiae almost smooth externally, front tibiae finely denticulate externally, tarsi 5-segmented and simple.