Aglenus brunneus (Gyllenhal, 1813)
There remains some doubt as to where this species originated; it was thought to have been native to the Nearctic region, where it is widespread, because it is occurs in synanthropic environments in Europe, but remains of the beetles, often in large numbers, occur repeatedly among historical remains from across Europe, including the UK, from early Roman times until relatively recently, and also from ancient Egypt. Therefore it is probably native to the Western Palaearctic, it now occurs throughout Europe as far north as the UK and southern Sweden, and is now cosmopolitan; having become widespread in North America since colonization and known from Iceland since the Middle Ages, it has been spread along with human movement and trade throughout the world. The UK distribution is sporadic across Wales and the south of England but it is difficult to find and probably very under-recorded; its natural habitat is among leaf-litter and decaying vegetation in wooded areas, under fallen timber or around the base of trunks just above or just below the soil surface, and it often occurs among accumulated animal remains etc in caves throughout the world, it is also synanthropic, although much less so than formerly due to improvements in housing etc, and occurs among compost, under hay, among manure, silage and hotbeds or among the residue from stored grains etc. and even in neglected cellars or among mouldy stored products. Adults occur throughout the year with most records from August to December, and both adults and larvae are known to feed on moulds and other fungi.
This species, variously classified among other families and recently transferred from Zopheridae, is very distinctive; small, 1.5-1.8mm, broadly elongate with the pronotum at least half the elytral length, near parallel-sided and entirely brown this species might only be confused with the eyeless bothriderid genus Anommatus Wesmael, 1835; here our 2 species are also tiny, 1.3-1.8mm, but they have rows of strong punctures to the pronotum and elytra and an apparently 1-segmented club; in Aglenus the pronotum and elytra are finely and randomly punctured and the antennal club is clearly 3-segmented.
1.5-2.0mm. Entirely dark to mid-brown with the appendages a little lighter. Very distinctive in outline; broadly elongate with projecting and acute elytral humeri and weakly rounded lateral margins. Entire upper surface glabrous and randomly punctured; head broad, only a little narrower than the pronotum, eyeless, with the antennae inserted laterally behind robust, curved and bidentate mandibles. Pronotum quadrate or slightly elongate, widest in front of the middle and with curved anterior angles, basal margin finely bordered and posterior angles distinct. Elytra curved and depressed at the base and evenly curved to continuously rounded apices that completely cover the abdomen, without any hint of striae. Legs narrow and short; tibiae only weakly broadened to the apex and without teeth or (obvious) spurs. Tarsi slender, without bilobed segments. Claws smooth and without a basal tooth.