Acrossus rufipes (Linnaeus, 1758)
This is perhaps the most widespread member of the genus, occurring throughout the Palaearctic and Asian regions, and introduced to Argentina, North America and Canada where it is now widespread and common. In the U.K. it is common to the far north of Scotland including the Western Isles and Orkney although records become more scattered and local with increasing latitude. Adults are active from April to October and are crepuscular and nocturnal; sometimes swarming over dung pasture in huge numbers in the evening and often coming to light far from suitable habitat e.g. in domestic gardens. They may be found in horse and cattle dung in just about any situation; they are often common in horse dung in woodland rides. A single pat may contain huge numbers, up to 1000 have been recorded. This is an early successional species and one of the first to arrive at fresh dung. Adults detect dung by smell. After arriving at dung the males stridulate using the wings against the abdomen to produce complex sounds which may last for up to 20 minutes and which play a part in courtship. Females possess similar adaptations but do not stridulate. Females begin ovipositing about a week after emerging; eggs are laid in groups of about 10 in the soil below or around the pat, the number laid is influenced by the density of beetles present and larval mortality is density dependent; in extreme cases the dung is consumed before they can fully develop. Larval development is slow and feeding continues into September or October, third instar larvae may feed in dung-lined chambers in the soil and are sometimes kleptoparasites of Geotrupes brood masses. Pupation occurs in the soil and the winter is usually passed in the prepupal stage although a few fresh adults also overwinter-these are obvious in the spring as they emerge with worn front tibiae. The peak of adult activity is late summer and autumn, and disturbing a pat at this time may attract huge numbers. Adults are often found infested with mites that will help to control mould as the pat ages.
The combination of colour, size and the form of the scutellum will identify this species. 9-14mm. Colour varies from dark brown to almost black; the head and pronotum are often slightly darker. The scutellum is approximately equilateral cf. Fossor, our other similar sized species. The clypeus is sharply angled in front of the eyes and more or less smoothly rounded anteriorly. Pronotum with large punctures scattered over a finely punctured surface. Elytral striae narrow, the interstices convex and finely punctured throughout. Appendages pale, the antennal club often markedly lighter. Male with prominent tubercles on the vertex.