Corylophus cassidoides (Marsham, 1802)

This species occurs from lowlands to low mountain altitudes throughout Europe from Spain to western Russia, extending north to the UK and southern Sweden and east to Turkey, Syria, Iran and Kazakhstan. Throughout the European range it is sporadic and mostly scarce but in some northern areas it may be locally common e.g. it is very common throughout Denmark but generally rare in Germany, in the UK it is very local and mostly coastal, occurring north to the Wash and Anglesey, although it is present across much of East Anglia and there are a very few inland records in the southern counties. Adults are present year-round, they are active over a long season from early spring and occur in fenland, permanently damp meadows and moors, and beside streams and ponds and they occasionally occur among damp decaying seaweed, they usually inhabit mouldy organic matter but may sometimes be swept from sedges or reeds etc. as they climb stems and foliage and take flight in the evening after hot summer days.  Through the winter they can be sampled by sieving or taking likely samples for extraction and they are sometimes present in flood refuse. Adults are mould feeders but otherwise little is known of the biology of this species.

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Adults are very small; about 1.0-1.1mm with females a little smaller than males, but this size coupled with the shape and colour makes them distinctive among our fauna. Elongate-oval and continuous in outline; broadest slightly behind the shoulders and evenly narrowed to more-or-less continuous elytral apices.  Head completely hidden from above, pronotum colour variable from dark with pale margins to extensively pale with only the disc darkened, elytra dark in the basal third then paler towards the apex. Legs entirely pale yellow, antennae pale with the club darkened. Antennae 11-segmented but with much reduced fourth and sixth segments so appearing 9-segmented, segments 8-11 forming a gradual but distinct club. Pronotum almost semi-circular from above, basal margin strongly sinuate and posterior angles acute, surface very finely and sparsely punctured and extremely finely pubescent (this only visible at high magnification), microsculpture isodiametric and faint. Mesosternum with a curved transverse ridge between the inner apical margins of the coxae. Scutellum transverse, triangular and curved laterally. Elytra without striae, finely and sparsely punctured but distinctly more strongly so than the pronotum, and with fine wavy microsculpture. Males can be distinguished by the form of the front tibiae which are indented and strongly curved just before the apex.