Oiceoptoma thoracicum (Linnaeus, 1758)

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POLYPHAGA Emery, 1886

STAPHYLINOIDEA Latreille, 1802

SILPHIDAE Latreille, 1806

SILPHINAE Latreille, 1806

Oiceoptoma Leach, 1815

This very widespread species occurs throughout the entire Palaearctic region except for the far north; it is locally common throughout Europe including some of the Mediterranean islands though absent from North Africa, and extends east through Russia, Mongolia and Siberia to China (Jilin and Heilongjiang provinces), South Korea, Taiwan and Japan. With the exception of the West Country it is widespread throughout mainland UK to the north of Scotland but generally absent from the islands and from Ireland, through much of this range it is very local and scarce but adults may be common where they occur and they may be under-recorded due to their lifestyle. Adults occur year-round and are active from April until September, they are associated with a range of decaying organic material but will usually be found on the carcasses of small mammals and birds, they are powerful fliers and may be among the first beetles to arrive at a carcass; at first they may swarm over it in numbers and take little notice of each other but eventually a pair will join up and mate and these will chase off the others and stand guard on the carcass to prevent others alighting. Eggs are laid under the carrion or in the surrounding soil and larvae emerge after a few days, coinciding with the first diptera larvae to emerge, and along with the adults they predate diptera larvae etc. but do not feed directly on the carrion. Larval development is rapid as is normal with such ephemeral food sources, pupation occurs in a cell in the surrounding soil and adults emerge soon afterwards. The species may be found in a wide variety of habitats from open moorland and dunes to woodland and scrub, adults are very good at detecting new carrion and may quickly fly over long distances to colonize it, hence they may suddenly appear in numbers at carrion traps or at rotting fungi etc. in fact anywhere with a good supply of insect larvae developing in decaying organic material, they are active by day and at night and occasionally turn up in flight-interception traps. Both adults and larvae, which resemble shiny dark woodlice with contrasting pale lateral margins, can move quickly and soon vanish into host material or into the soil when disturbed, and both can produce a disgusting oral defence fluid when alarmed or handled.

Oiceoptoma thoracicum 1

Oiceoptoma thoracicum 1

Adults are very distinctive and should not be confused with any other UK species; the habitus and colour are sufficient for a confident identification. 11-16mm. Long-oval and flattened in form, entirely dark grey to black but for the orange or red pronotum. Head narrow and quadrate or nearly so, with small and convex eyes, finely and densely punctured vertex and frons and long antennae terminating in a four-segmented club. Pronotum transverse and curved laterally from rounded anterior and posterior angles, apical and basal margins widely produced and the surface irregular and widely explanate, pubescence dense and randomly oriented. Scutellum large and triangular with sinuate lateral margins and very finely punctured and pubescent surface. Elytra sub-parallel and evenly curved to a continuously rounded apical margin, surface irregular and lacking striae, each with three variously-developed fine longitudinal ridges and broad explanate margins. Legs long and slender, all tibiae with rows of fine spines throughout, front tibiae hooked at the internal apical angle, middle and hind tibiae with a long terminal spur. Tarsi 5-segmented; basal segment of front tarsi and basal and terminal segments of middle and hind tarsi elongate, male front tarsi broader than those of the female. Claws large and curved, smooth internally and without a basal tooth.