Cis fagi Walt, 1839
Care must be taken with this species as it keys to C. castaneus Mel. in Joy and is variously referred to as C. fuscatus Mellié, 1849 in the literature. It is widespread and generally common throughout Europe from Spain to Greece and Asia Minor and north to the UK and central provinces of Fennoscandia, the eastern limit of the distribution is Ukraine and certain regions of western and northern Russia as far as Moscow. In common with many saproxylic species it is thought to have declined in northern areas of Europe over recent decades due to exploitation and fragmentation of forest areas. Here it is locally common throughout England and Wales north to the Humber though scarcer in the south-west and generally rare further north to the Scottish border. Adults are present throughout the year, they occur in fungi on various trees in deciduous woodland and wooded parkland etc, including alder (Alnus glutinosa (L.)), aspen (Populus tremula L.)and other poplars, birch (Betula L.), oak (Quercus L.), beech (Fagus sylvatica L.) and willow (Salix L.), and in northern Europe also from pine (Pinus L.) and Norway spruce (Picea abies (L.) H. Karst.) Larvae develop among mycelia in decaying wood; in the UK the main host fungus is Laetiporus sulphureus (Bull.) Murrill (1920), especially among mycelia in decaying red oak xylem, but they have also been recorded from Fomitopsis betulina (Bull.), Inonotus dryadeus (Pers.:Fr.) Murr., Ganoderma applanatum (Pers.) Pat. and species of Armillaria (Fr.) Staude. In northern Europe they have also been recorded from Fomes fomentarius (L.) Fr. 1849, Trichaptum abietinum (Dicks.) Ryvarden (1972) on spruce and T. fuscoviolaceum (Ehrenb.) Ryvarden (1972) on pine. Adults are nocturnal and may sometimes be found active on fungi or on nearby bark at night, but the easiest way to sample them is to take fungus samples for extraction, older and slightly decayed samples are best and any saproxylic species is worth trying. The beetles may be sampled year-round but are most common in spring and autumn.
Cis fagi 1
© Lech Borowiec
1.3-1.9 mm. Long-oval and convex, entirely pale to dark brown including the appendages, dorsal surface fine, moderately dense punctures and short semi-erect scales throughout. Head transverse from above, with protruding convex eyes and prominent robust mandibles, frons and clypeus almost flat; the male clypeus with two small blunt tubercles. Antennae 10-segmented, the third longer than the fourth and the last three segments form a loose club, the club may be a little darker than the funiculus but it is still pale brown. Pronotum very slightly elongate, broadest near the middle and rounded anteriorly where it hides the lateral margins from above, posterior angles rounded and basal margin evenly curved, surface convex and without structure. Lateral margins with a fringe of fine setae which are distinctly longer than the narrow explanate margins. Scutellum rounded apically. Elytra slightly narrower across the base than the width of the pronotum, with rounded shoulders and smoothly curved to a continuous apical margin, surface evenly convex and punctured, about the same as the pronotum; the punctures equal in size and each bearing a short but obvious scale-like seta. Front tibiae produced at the apex to a sharp external tooth, middle and hind tibiae simple.