Tachinus marginellus (Fabricius, 1781)
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POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
TACHYPORINI MacLeay, 1825
Tachinus Gravenhorst, 1802
A very widespread Palaearctic species known from Europe and Asia Minor to the far east of Russia. In Europe it occurs from Portugal to Italy and Greece in the south and is present on many of the Mediterranean islands, and to the north it extends to the far north of Norway, Sweden and Finland. The species occurs from lowlands to the upper limit of the tree-line in mountain regions; it is generally abundant in central and, more especially, northern regions and it is among the most frequently-recorded members of the genus. The nominate subspecies occurs throughout the range while ssp. angelini Schülke, 1996 is widespread in Central and Southern Italy, and ssp. rufulus Sahlberg, 1876 is widespread in Fennoscandia. Generally common across Southern and Central England and Wales, less so further north to Orkney and the Western Isles, and widespread though very local in Northern Ireland, it is the most frequently recorded of the UK species after T. rufipes (Linnaeus, 1758). Adults are present year-round; they overwinter among decaying vegetation, under debris or in the soil, and are active from March until November, they peak in abundance during June and July and often again in the autumn. The species is often associated with herbivore dung and it is frequently abundant on grazing pasture, but it also occurs among decaying vegetation in a wide range of habitats including disturbed sites such as waste ground, farms and agricultural land and domestic gardens, it also occurs in old mammal and bird nests and decaying fungi, adults sometimes occur at sap on warm summer evenings, and they occasionally occur at carrion. Adults are generally nocturnal but even so they are rarely seen in the open; they usually remain hidden within host material although they may be seen alighting on freshly deposited dung in hot sunny weather. They can be sampled by sieving suitable material, and here old hay or straw is often ideal, or using dung-baited or pitfall traps in any situation, decaying terrestrial fungi may host large populations, and they may appear among extraction samples at any time.
3.5-5.0 mm. Elongate, rather parallel-sided and, compared with many members of the genus, somewhat narrow, body shiny black with pronotal and elytral margins and terminal abdominal tergite(s) reddish-brown, antennae black with several basal segments brown, legs entirely brown. Head transverse, broadest across small and prominent eyes and with long converging temples (usually substantially hidden), cheeks converging to a smoothly rounded apical margin, surface smoothly convex and finely punctured. Terminal maxillary palpomere as long as and at most only slightly narrower than the previous segment. Antennae long and slender with all segments elongate. Pronotum transverse, about 1.5X broader than long, and at most only as broad as the elytra, broadest across rounded posterior angles and narrowed to slightly projecting anterior angles, surface evenly convex, finely punctured throughout and without microsculpture. Pronotal colour varies; the lateral margins are usually narrowly red and this may extend around the basal margin, but the apical margin and the centre of the basal margin is usually at most only very narrowly or vaguely paler. Elytra quadrate or nearly so, about 1.25X longer than the pronotum, and parallel-sided or slightly dilated from rounded shoulders to recurved apical margins, surface without striae, finely punctured throughout (usually a little stronger so than the pronotum), and without microsculpture. Lateral and apical elytral margins pale, often broadly so. Abdomen long and gradually tapering from the base, basal tergites strongly bordered, evenly convex and with a small patch of dense pubescence either side of the middle, apical tergites with long outstanding setae. Last visible tergite distinctive in both sexes. Legs long and slender, tibiae hardly broadened from the base, front tibiae with fine spines along the external margin, middle and hind tibiae with groups of strong spines and short apical spurs. Tarsi 5-segmented, basal segment of hind tarsi only slightly longer than the second segment. Front tarsi dilated in males.