Hylotrupes bajulus (Linnaeus, 1758)
House Longhorn Beetle
POLYPHAGA Emery, 1886
CHRYSOMELOIDEA Latreille, 1802
CERAMBYCINAE Latreille, 1802
CALLIDIINI Kirby, 1837
HYLOTRUPES Audinet-Serville, 1834
A monotypic genus comprising the widespread Palaearctic H. bajulus (Linnaeus, 1758) which, following introductions, is now established in North America and South Africa. In the U.K. it is very local in the south east of England where it occasionally infests timber in buildings and very occasionally the decaying stumps of conifer trees in the wild. It is so named because through much of its range it is synanthropic, developing in dry structural timber of sufficient size and in the past it has been a common pest in parts of Europe. In the wild a range of conifer trees are hosts e.g. Pinus, Picea or Abies etc. Adults generally emerge in early summer and may persist until September, often being seen in numbers inside buildings where they tend to remain. Eggs are laid in small groups in crevices or cracks in dry wood and the larvae initially feed in the sapwood, tunnelling deeper as they grow; the galleries are packed with sawdust and frass and in severe infestations the timber may be completely reduced to a shell with the surface intact so that structural failure may occur before the beetles are suspected. Larval development takes between 2 and 10 years depending upon the temperature and moisture content of the wood. Pupation occurs just beneath the surface of the wood, generally in the spring, and under ‘normal’ conditions the life-cycle takes 2 or 3 tears.
Despite the great variation in size, 7-21mm, this species is very distinctive and should not be confused with any other; within the Callidiini it is unique in having the anterior coxae completely separated by the Prosternal process and the third antennomere longer than the fourth and fifth combined. The species is shiny and drab coloured; black to mid-brown, with an oblique patch of dense pubescence about a third from the elytral base. The dorsal surface is clothed with long pale pubescence which is thickest on the pronotum and progressively sparser towards the apex. Head robust, very finely and densely punctured, with short antennae; in the male almost reaching the middle of the elytra, in the female overlapping the shoulders. Mandibles sharply pointed and sinuate along the inner margins. Eyes narrow and elongate; enveloping the posterior margin of the antennal tubercles. Pronotum rounded and strongly sinuate before the laterally protruding hind angles, the anterior margin incurved and the posterior margin straight. The surface is variously punctured with a smooth longitudinal mid-line and a wide and smooth tubercle either side of the middle. Elytra sub-parallel, a little wider in the female, with prominent shoulders and rounded apices; the surface strongly rugose and randomly punctured, and each with an indistinct raised longitudinal carina. Legs robust; femora swollen, the tibiae relatively long and slender and each with a fine spine on the inner apical angle. Basal tarsal segment elongate, third deeply bilobed and hiding the fourth, the fifth elongate. All claws with a weak basal tooth.