Margarinotus striola (Sahlberg, C.R., 1819)
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POLYPHAGA Emery, 1886
HYDROPHILOIDEA Latreille, 1802
HISTERINAE Gyllenhal, 1808
Margarinotus Marseul, 1854
This locally common species occurs throughout Europe from the Mediterranean north to the UK and above the Arctic Circle in Fennoscandia, it extends south to Greece and east through Asia Minor, Ukraine and Russia into Siberia and occurs very locally in Japan (Hokkaido). Throughout most of the European range, north to the UK and the south of Sweden, it is represented by ssp. succicola (Thomson, C.G., 1862) but from the northern Baltic coast and into Fennoscandia and northern Russia it is mostly represented by the nominate subspecies. These subspecies differ very subtly in morphology but are readily distinguished by the shape of the median armature of the male genitalia. Adults are present year-round and are active over a long season from early March until October or November, they generally occur in open habitats, especially grassland and scrub, and will often be found in disturbed habitats such as gardens or urban parkland. Typical haunts are among decaying vegetation such as compost and damp straw and they sometimes occur in dung but they are strongly attracted to carrion and they are also strong fliers and so may arrive at a carcass in almost any situation soon after it begins to decay. Little is known of the biology but both adults and larvae are predatory and are known to feed on diptera larvae and mites, and larvae are known to develop rapidly among carrion and dung, which is to be expected among aggressive competition for an ephemeral food source. Large populations of adults may be sampled through the spring and summer using carrion traps, and they will often be found among large decaying bracket fungi in the autumn.
Medium sized beetles, 5.5-7.0mm, broadly oval and convex in form and entirely shiny black, only the antennae and sometimes also the tarsi partly red. Adults may be recognized among our fauna by the presence of doubled marginal striae on the pronotum, at least 5 larger teeth on the outer margin of the pro-tibia, an elytral depression at the base of the third stria and the form of the stria behind the eyes. Head slightly transverse with eyes only narrowly visible from above and robust, forwardly-produced mandibles, frontal stria deeply impressed and angulate medially, sometimes incomplete, vertex and frons smooth and very finely punctured. Antennae inserted above a small scrobe near the base of the anterior margin of the eyes, usually black with the base of the scape and the funiculus red. Pronotum convex and widely transverse, marginal stria widely interrupted anteriorly and extending into the basal third (at least) laterally, inner stria complete anteriorly and extending into the basal fifth, surface smooth and very finely punctured, sometimes with slightly stronger punctures or a small depression in front of the scutellum. Prosternum produced anteriorly into a broad rounded lobe which projects beneath the head, prosternal process broadly triangular apically, and with broad and deep antennal cavities beneath the anterior angles. Elytra broadly transverse and more or less continuous in outline with the pronotal base, lateral margins smoothly rounded and apical margins separately rounded and truncate, epipleura strongly and densely punctured, interstices smooth and very finely punctured, striae usually well-impressed; two inner striae present only in the apical half (or so) and there may be a trace of a third in the apical third, the next four more or less complete, humeral stria short and oblique, the next (the internal sub-humeral stria)long but terminating under the humeral stria and before the apex, and the outermost stria (the external sub-humeral stria) extending from near the base to at least the middle. All tibiae broadly expanded towards a truncate apex and all with a long and sharp spur at the inner apical angle, middle and hind tibiae with series of stout spines along the outer margin, external margin of fore tibiae with five larger teeth in the apical half and several smaller teeth, which may be absent or substantially worn, towards the base. Tarsi 5-segmented, pro-tarsi simple, basal segments of middle and hind tarsi lobed below and with a sharp spine at the apex of each lobe.