Acrulia inflata (Gyllenhal, 1813)
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POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
OMALIINI MacLeay, 1825
Acrulia Thomson, C.G., 1858
This is a mostly Western Palaearctic species although it has also been recorded from Kazakhstan and Siberia; it is widespread across Europe from the Pyrenees to Central Italy, the Balkan Peninsula, Greece and Ukraine, and extends north to the UK and above the Arctic Circle in Fennoscandia. In southern and central parts of Europe it is very local and rare, with most records from mountain areas (to 2000 m.), while in the north it becomes locally common, especially in extensive areas of older woodland. In the UK it is locally common throughout Wales and Central England from the Severn catchment to North Yorkshire, there scattered records from the Scottish Highlands and a very few from the south of England and Southern Ireland. Across southern and central Europe it is associated mostly with a range of broadleaf trees while in the north it occurs more frequently in conifer woodland, especially on Pine (Pinus sylvestris L.) and Spruce (Picea abies (L.)) although in the UK it has been recorded from a range of both broadleaf and coniferous trees. Adults occur year-round, peaking in abundance during June and again in September and October, they occur under loose bark and among decaying wood, less often among leaf litter or in fungi and at sap, and on the continent sometimes at carrion. Little is known of the biology but adults are probably predatory (typical of the group) and, from the phenology, breeding is likely to occur in spring and early summer. Searching under bark or taking samples of decaying wood are probably the best ways to find adults but they have also been recorded from a range of sporocarps including Trametes hirsuta (Wulfen) Lloyd (1924), Pycnoporus cinnabarinus (Jacq.( P.Karst. (1881), Gloeoporus pannocinctus (Rommel) J.Erikss(1958), Neontrodia infirma (Renvall & Niemelā) Audet (2017) and species of Cerrena Gray (1821), and this may well be where the larvae develop.
2.0-2.5 mm. Elongate-oval and discontinuous in outline, body shiny dark brown with paler margins to the pronotum and elytra and substantially pale abdomen, antennae dark brown, usually with segments 2-7 a little paler, legs dark brown with paler tarsi. Head moderately strongly but not densely punctured, rather flat and with an indistinct transverse impression between the eyes, eyes small and strongly convex, temples short and strongly converging, frons produced and angled at the lateral antennal insertions. Penultimate maxillary palpomere short and expanded towards the apex, terminal segment long and narrow. Antennae 11-segmented; segments 3-6 narrower than the two basal segments and segments 7-11, segments 9 & 10 strongly transverse. Pronotum transverse and broadest about the middle, narrowed to slightly protruding anterior angles and sinuate before almost perpendicular posterior angles, lateral margin finely crenulate (most obvious about the middle), surface evenly convex, without impressions and punctured about the same as the head. Elytra quadrate or nearly so and much longer than the pronotum, gently curved from rounded shoulders to a truncate apical margin, surface without striae and strongly and rather densely punctured. Abdomen shorter than the elytra, usually with 6 exposed tergites and rounded and gradually narrowed to the apex. Legs short and slender. Tarsi 5-segmented, the terminal segment at least as long as 1-4 combined, basal segments of front tarsi transverse and simple, without a ventral fringe of setae.
Acrulia Thomson, 1858
This small genus of rove beetles is restricted to the Palaearctic region, several Nearctic and Eastern Palaearctic species formerly included are now assigned to a separate genus, Acruliopsis Zerch, 2003. The European fauna included only three species and of these only one is widespread; A. punctata Coiffait, 1978 is endemic to France, A. angusticollis Reitter, 1909 is endemic to Croatia while A. inflata (Gyllenhal, 1813) is widespread in the west and probably occurs throughout the region. The genus is characterised by the elongate, convex and oval body form, the long terminal maxillary palpomere, dentate lateral pronotal margins and long terminal tarsomere. The species are mostly saproxylic and often associated with fungi.