Agrilinus ater (De Geer, 1774)
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POLYPHAGA Emery, 1886
SCARABAEOIDEA Latreille, 1802
APHODIINI Leach, 1815
Agrilinus Mulsant & Rey, 1870
A widespread and generally common species throughout central and northern Europe extending to the far north of Scandinavia and the U.K. although it appears to have declined in recent decades. Here it is common and often abundant throughout England and Wales, becoming less so further north to Orkney, Shetland and the Western Isles. Adults occur year-round, sometimes appearing in flood-refuse during the winter, and become active a little later than other spring species, usually from early April and peaking in abundance in May and June, later they persist in smaller numbers although there may be a brief period of abundance in late summer or autumn. The typical habitat is open pasture where they develop in the dung of various cattle, sheep and horses etc. although they also occur in decaying vegetation and during the spring when they disperse may be netted in flight or attracted to light almost anywhere. They almost always occur among populations of other common species e.g. A. prodromus (Brahm, 1790) or A. sticticus (Panzer, 1798) and are mid-successional species, arriving at dung when it is a few days old; males will rest on the dung and stridulate to attract females, and mating occurs on the surface of the dung. Females choose dung already colonized by other coprophagous insects but will avoid pats hosting large populations of Scatophaga larvae, they oviposit in drier parts of the dung and adults of both sexes will generally be found just under the crust, the number of eggs laid in a particular pat decreases as the number of other larvae present increases. Larvae develop in drier parts of the dung and where there is competition for food the resulting adults may be lighter and, as the number of eggs produced correlates with female body size, less fecund, and so numbers may vary widely from year to year according to host availability and competition. Larvae develop through the spring and summer with pupation occurring in the ground beneath the host from mid to late summer. New generation adults eclose from late summer and either become active and feed for a while or remain underground through the winter. Maturation feeding continues when they emerge in the spring.
4-6mm. Entirely black or, occasionally, with the elytra obscurely red. Vertex with 3 tubercles, the central tubercle much larger than the others in the male, clypeus narrowly expanded in front of the eyes; rounded and then sinuate to the anterior angles, anterior margin distinctly curved, in the male with a raised transverse ridge. Pronotum shiny and evenly convex, without sculpture, punctation even throughout with a mix of large and small punctures, lateral and basal margins bordered. Scutellum equilateral with large punctures and microsculptured as the elytra. Elytral interstices finely punctured throughout, with variable but usually strong reticulate microsculpture so appearing dull against the pronotum. Striae shallow and variously punctured, usually distinctly so towards the base, and shiny throughout. Legs entirely dark. Basal segment of the metatarsi as long as the next 3 combined.
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Very similar to several other dark Aphodius species but ater soon becomes obvious in the field; the elytral apices are microsculptured and dull so contrasting against the shiny striae, and the elytra usually contrast against the shiny pronotum. In ater there is a fine longitudinal carina between the mesocoxae, a character missing in the similar A. borealis Gyllenhal, 1827, A. constans Duftschmid, 1805, A. nemoralis Erichson, 1848 and A. lapponum Gyllenhal, 1808. In the common and widespread A. granarius (Linnaeus, 1767) the explanate elytral margin is much broader towards the apex than in ater.