Anotylus tetracarinatus (Block, 1799)
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POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
OXYTELINI Fleming, 1821
This is a generally common and often abundant species throughout almost the entire Palaearctic region, it occurs throughout Europe from lowlands to the alpine zone and to above the Arctic Circle in Scandinavia and is often the most common member of the genus in southern and central areas, it is widespread across North Africa and the Near East and following introductions is now established in eastern Canada and the United States including Alaska. Here it is generally abundant throughout England and Wales although less so in the north and largely absent from the West Country, it is vary local and scarce further north to the Scottish Highlands and from Ireland it is known from only a few records in the north. Adults occur among decaying fungi and plant material, usually on dry grassland, and through the summer they are often very abundant in herbivore dung, they fly well and disperse in the afternoon or evening when the temperature drops; they sometimes form swarms of thousands of individuals and may travel or be carried by the wind over long distances and so may occur among suitable host material in just about any not-too-wet situation. They are active over a long season from early spring and peak in abundance during late May and June and again, though much less so, in late summer and autumn when very large numbers may occur in decaying terrestrial bracket fungi, they are otherwise common in mammal nests, compost, hay and straw etc. and on the continent are regularly recorded from accumulated organic matter in caves. Both adults and larvae are predatory and larvae develop among decaying organic matter, more especially in herbivore dung, they appear from early spring and develop quickly as new-generation adults occur from May. Adults may be sampled using dung-baited traps or by immersing dung samples and collecting them as they escape, but they will usually appear in numbers when sweeping insects in flight over dung pasture, they also come to light and occur among suitable flood-refuse samples through the winter.
1.8-2.5mm. Entirely dull black or with the elytra variously brown, legs pale brown or with darkened femora, and antennae substantially dark brown. Head transverse with small, weakly convex eyes and long, slightly curved temples, the surface, except for a narrow shiny area around the clypeus, with dense cellular microsculpture, antennae short with the basal segment evenly expanded from the base and segments 5 to 10 transverse. Pronotum transverse with smoothly curved margins and posterior angles, the anterior angles distinct and the lateral margins not crenulate, surface densely microsculptured, with three longitudinal furrows, the delimiting ridges also granular, and widely depressed laterally. Scutellum heart-shaped and with a variable median keel. Elytra transverse and slightly widened towards rounded apical angles, the surface finely and randomly punctured and pubescent. Abdomen with very weak cellular microsculpture and moderately dense, slightly raised punctures that give a wrinkled appearance at high magnification. Legs short and slender, external margins of tibiae with at most a single row of very fine spines, margins of the front tibiae only weakly curved and the apex entire i.e. without an external indentation-this is an important character as several superficially similar species have the outer margin strongly indented before the apex. Tarsi 3-segmented.