Megarthrus depressus (Paykull, 1789)
This Palaearctic-wide species is generally common and often abundant from lowlands to alpine altitudes throughout Europe from the Pyrenees to Italy and Greece in the south, and north to the UK and northernmost provinces of Fennoscandia, it seems to be absent from the Mediterranean islands and it does not occur in North Africa. With the exception of the West Country the species is generally common throughout England and Wales, and less so and rather local further north to Orkney and across Northern Ireland. Adults are present year-round; they overwinter among compost or decaying litter etc, and are active from March until November, peaking in abundance during late spring and early summer. The species may be expected from any type of decaying vegetation; they are often abundant in compost, especially when this is fermenting and warm, leaf-litter, old and dry dung, reed litter, old bird nests, sporocarps on decaying trunks and stumps, among undisturbed matted grass etc, and they may be very common among decaying terrestrial fungi in the autumn. The usual habitat is damp grassland, wetland margins and open woodland, but they are often present in disturbed sites such as domestic gardens, wasteland and parkland. Little is known of the biology but both adults and larvae are thought to be saprophagous and/or mycophagous, and reproduction and larval development probably occur in spring and early summer. Adults may be sampled by sieving or extracting samples of likely material, they are generally not recorded from light but they often occur in flood refuse, and usually in numbers.
2.5-2.8 mm. Broad, flattened and dull, dorsal surface very finely pubescent, head black, pronotum and abdomen black to dark brown, often slightly paler reddish around the margins, elytra reddish-brown, antennae entirely dark or with the basal segment slightly paler, legs entirely pale reddish-brown to yellowish. Head uneven and finely-punctured between convex and protruding eyes that occupy most of the lateral margin, clypeus produced in front of the eyes and rounded anteriorly. Antennae inserted at the lateral clypeal margin, 11-segmented with two large basal segments, segments 3-5 elongate and narrow, 6-10 broader and quadrate or nearly so, and the terminal segment elongate and oval. Pronotum transverse, lateral margin rounded or very obtusely angled to incised posterior angles, apical margin weakly recurved, basal produced medially and sinuate before the lateral incision. Pronotal surface finely and moderately densely punctured throughout with a single median groove and wide explanate margins. Elytra transverse and much longer than the pronotum, dilated from rounded shoulders to slightly curved apical margins, lateral margins narrowly explanate and almost straight, surface without striae, finely and evenly punctured throughout. Basal abdominal tergites strongly bordered, penultimate tergite broad and widely rounded, last tergite small and triangular, entire abdomen finely punctured. Legs long and slender, tibiae not thickened from the base, and tarsi with five simple segments. Males may be distinguished by the strongly-curved middle tibiae.
Megarthrus depressus 1
Megarthrus depressus 2