Corticaria impressa (Olivier, 1790)
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POLYPHAGA Emery, 1886
CUCUJOIDEA Latreille, 1802
CORTICARIINAE Curtis, 1829
Corticaria Marsham, 1802
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This very widespread species is locally common throughout much of Europe and extends east through Russia, Turkey and Kazakhstan to the far east of Russia and Japan, in Europe it extends from the Mediterranean north to the UK and above the Arctic Circle in Fennoscandia. In North America it was first recorded from Nova Scotia in 1983 (although there are two records from 1951 from British Columbia but the species appears not to have become established here) and has since become established and widespread across north-eastern North America. In the UK it is generally common in south east and central England, mostly coastal in Wales and very local and sporadic further north to the Scottish Highlands and in Northern Ireland. Adults occur year-round; they overwinter under bark or among damp organic material and are active nocturnally over a long season from early spring. Typical habitats are damp woodland and carr where they have been recorded from a wide range of trees including Norway Maple (Acer platanoides L.), birch (Betula L.), aspen (Populus tremula L.) and other species of Poplar, oak (Quercus L.), elm (Ulmus L.), willow (Salix L.) and spruce (Picea Mill.), and locally we have found them abundantly on Hazel (Corylus avellana L.) and Elder (Sambucus nigra L.), and they also occur among decaying organic matter such as hay and straw and leaf litter and have been found under decaying seaweed on beaches in the south east. In Canada the majority of records are from seashore and other coastal habitats and they have also been found in funnel traps in pine woodland. Larvae are thought to develop through the spring and summer in much the same habitats as the adults, both adults and larvae very probably feed on fungal spores, which is typical of the family, but we have observed numbers of adults grazing lichens on decaying hazel bark. The best way to find the species is to search very carefully among decaying bark; they often occur on twigs or small branches with areas bark missing and they are cryptic, slow-moving and can be very difficult to spot, they also vanish into crevices or among debris and lichens when disturbed. Through the winter they sometimes occur among extraction samples from a range of habitats e.g. we had several specimens during December 2012 from an old moorhen nest.
Adults are tiny, 1.8-2.4 mm, elongate and discontinuous in outline, entirely dark brown with paler brown appendages, and finely pubescent throughout. Head transverse, with convex and coarsely-faceted eyes and short, obtusely-angled temples, surface evenly punctured and weakly convex, without a median impression. Antennae 11-segmented with a long and loose club; the ninth segment gradually broadened from the base and widest just before the apex. Pronotum transverse and widest about the middle, lateral margins evenly curved and clearly denticulate, anteriorly smoothly rounded, posterior angles obtuse, basal margin almost straight and surface evenly but not densely punctured, about the same as the head, without structure but for a well-defined median basal fovea. Elytra elongate-oval with sloping shoulders and a continuously curved apical margin, striae strongly punctured almost to the apex, interstices convex and very finely punctured, across the base with five or six rows of punctures between the suture and the humerus, pubescence decumbent. Legs short but robust, femora broad and smooth, tibiae narrow, without internal teeth or angles and each with a tiny terminal spur. Tarsi 3-segmented; the basal segments short and lobed and the terminal segment long and curved, all claws with a strong internal tooth. Males may be distinguished by a small tooth at the apex of the front and middle tibiae, in females they are simple.