Geostiba circellaris (Gravenhorst, 1806)
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POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
ALEOCHARINAE Fleming, 1821
GEOSTIBINI Seevers, 1978
Geostiba Thomson, C.G., 1858
This is a locally common species throughout Europe from France to Asia Minor and north to the UK and the far north of Fennoscandia, it is present on many of the Mediterranean islands but not in North Africa, to the east it extends into eastern Siberia and North Korea, and has become established in North America following introductions from Europe. In the UK it is generally common throughout England and Wales and more local further north to the Scottish Highlands and the Outer Hebrides, and it is locally common in Northern Ireland. Adults occur year-round, they are active through the winter and peak in abundance during spring and autumn. Typical habitats are damp deciduous woodland and wooded parkland where they occur among decaying leaf-litter, often on heavy acidic soil and usually among populations of other small staphs, but they may also occur under matted vegetation in damp grassland situations. Little is known of the biology but adults are known to fly and sometimes swarm in the spring, during the winter we have recorded them from old bird nests in deciduous woodland, dry reed litter, composted sedges beside reed beds and in an old decaying straw bale on a reservoir margin, and they are probably mainly nocturnal as they we found them in numbers on the surface of large decaying terrestrial bracket fungi during the autumn and winter in local woodland. Sampling is easiest by sieving leaf-litter but they occur in extraction samples through the winter and decaying fungi will sometimes produce them in numbers, usually along with numerous other small staphs. Adults may be found parasitized by the fungus Monoicomyces homalotae Thaxt. (Laboulbeniaceae), a specialist that develops on Geostiba and various Atheta Thomson, 1858.
2.0-2.8 mm. Pale brown with the head and several subapical abdominal segments darker brown, legs pale brown, antennae extensively dark but usually with several basal segments pale. Head broadest in the basal third and much narrower than the pronotum, with small weakly convex eyes and long rounded temples, surface evenly convex with oblique pubescence on the disc and more dense, longitudinal pubescence behind the eyes, punctures very fine, microsculpture transverse and wavy, very fine and only visible at high magnification. Penultimate maxillary palpomere long and fusiform, terminal segment diminutive. Antennae 11-segmented, segments 1-3 elongate; the second a little longer than the first, 4-6 weakly transverse, 7-10 more strongly so, terminal segment slightly longer than 9 & 10 combined and rounded apically. Pronotum narrower than the widest part of the elytra, broadest at or slightly in front of the middle, slightly transverse, rounded apically and with rounded or indistinct posterior angles, surface very finely punctured and with fine pale pubescence that tends to lie longitudinally on the disc and form wavy longitudinal lines laterally, surface evenly flattened, at most with two indistinct impressions in front of the basal margin. Elytra transverse and shorter than the pronotum, with rounded shoulders and dilated apically, posterior margin sinuate before distinct angles, surface more strongly punctured than the pronotum and with pale pubescence that forms long wavy patterns. Males have a tubercle at the base of each elytron, near the scutellum. Abdomen strongly bordered, slightly dilated about the middle and not strongly narrowed apically, tergites 1-3 impressed across the base, 4-6 smoothly convex, all finely punctured and pubescent, more sparsely so towards the apex, microsculpture transverse and very fine. Legs long and slender with the posterior femora longer and more robust than the others, tibiae without isolated erect setae on the outer margin or distinct apical spurs. Tarsi 4-5-5, basal segment of hind tarsi almost as long as the next two segments, terminal segment of all tarsi long and slender. Claws smooth and without a basal tooth.