Thes bergrothi (Reitter, 1880)

Native to northern Europe from France to the Baltic and south to northern Italy, this species has been transported with foodstuffs and is now established in many countries worldwide, it was first recorded in North America in 1948 and is now established across Canada, it has been recorded from the far north of Europe and is known from introductions in Iceland and Greenland although the eastern limit of its distribution is Moscow. It is very local and generally rare in the wild, it is has been recorded across Europe from decaying trees and fallen timber, old bird nests and among decaying plant remains  but it is more generally synanthropic, occurring in damp and dark undisturbed places such as warehouses, sheds, basements and among straw, hay and animal feeds. Beyond Europe it always occurs under artificial conditions, there have been a few widely-scattered records in the UK since the early 20th century where adults have occurred in a wide variety of situations; among stored cocoa, flour, cheese and dried ‘Chinese Rhubarb’, on old boots in a cellar, on walls under damp wall paper, in Canada and Europe they have occurred in much the same conditions as well as among mouldy wine vats and stored dates etc, and they are likely to occur in damp and mouldy conditions indoors generally. Adults often occur in numbers and when swarming have been found at windows and exposed on walls. larvae have been found during the summer and reared to adults on damp bread, they are photophobic and feed within or under host material, pupation occurs within or near to host material and freshly-eclosed adults have been recorded in late summer and autumn.

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​1.8-2.5mm. Forebody narrow compared to the broadly-oval elytra, entirely brown and glabrous but for sparse very small setae visible only at high magnifications. Head densely and often confluently punctured, eyes convex, small and prominent, cheeks and temples long and near-parallel-sided and labrum weakly curved anteriorly, almost truncate. Antennae inserted laterally outside the margins of the labrum, 11-segmented; the basal segment large and curved internally, second segment quadrate, remainder elongate, 9-11 forming a narrow and loose club. Pronotum transverse, broadest in the apical third and narrowed to a strong sub-basal constriction, anterior angles weakly produced forward and apical margin curved, surface transversely impressed before the base and with two median carinae extending from the base to at least the middle, punctures strong close throughout, lateral margins raised and finely crenulate. Elytra with slightly produced humeral angles and smoothly curved to a continuously-rounded apical margin, surface with double rows of strong punctured between raised interstices, the fifth and seventh carinate to beyond the middle, and the lateral margin explanate almost to the apex. Legs long and slender, femora unarmed, tibiae smooth and lacking apical spurs. Tarsi 3-segmented, the basal segments short and lobed ventrally, apical segment long and curved. Claws smooth and without a basal tooth.