S. cylindricum (Linnaeus, 1758) is a widespread Palaearctic species distributed from northern Spain and France across Northern and Western Europe, including the south of Scandinavia, to Russia. In recent decades there has been a decline in the range and abundance of this species due mostly to the destruction and exploitation of forested areas and changes to the proportions of tree species. The species is now extinct in some countries and protected in some others. In the U.K. it is our most widely distributed Lucanid occurring throughout England and Wales and sporadically in Ireland and through Scotland north to the highlands. Sinodendron is active both by day and night; searching by torchlight will often produce the species, more often than not males, on trunks and fallen timber. When found, males should be observed carefully as the sexes cooperate in breeding; males usually guard the entrance to a brood tunnel while the female excavates. The tunnel is usually branched, with many egg laying chambers packed with wood dust. Mating occurs within the tunnel. Larvae live for up to three years and construct pupal chambers close to the surface. We have observed adults emerging from the surface of an Aesculus stump in Cassiobury Park in June. Brood tunnels may be constructed on trunks or branches up to four metres high. The wood is usually dry with some signs of decay but we have seen them boring into a fallen and thoroughly damp Fagus trunk by the canal in Watford. Typical hosts include Tilia, Fraxinus, Aesculus, Malus Spp, Castanea sativa, and Salix and they have been recorded from Pinus but they seem to have a preference for Fagus. The species is common in suitable habitats locally; in general we see them on wood that has been damaged or to some extent decayed but we have seen them boring into damaged parts of otherwise healthy Betula and Aesculus. During the day they may be found basking in hot sun on logs or trunks, and on several occasions we have found them under loose and powdery bark on old Betula stumps. Sometimes they may be seen in flight, generally in wooded areas or above open ground at wooded margins, and usually a single specimen is observed but on one occasion at Aldbury in the Chilterns we sat for about twenty minutes in a Fagus wood above a calcareous hillside watching dozens of both males and females flying in all directions. In flight the red upper-surface of the abdomen is distinctive.