Xestobium rufovillosum (De Geer, 1774)
POLYPHAGA Emery, 1886
BOSTRICHOIDEA Latreille, 1802
ERNOBIINAE Pic, 1912
Xestobium Motschulsky, 1845
This is a native and generally common species of temperate woodland throughout the Palaearctic and Asian regions and, because of the xylophagous and long-lived larval stage, it now has an almost cosmopolitan distribution, occurring in structural and ornamental hardwood wherever these are imported from suitable areas. It is a widespread adventive species in the United States and Canada. In the U.K. it is common throughout England north to South Yorkshire, becoming more scarce and sporadic further north. The species is a notorious pest of structural timbers, and sheltered indoor situations seem to favour its development provided the host timber has a moisture content of at least 14% and contains fungi that the larvae can use as a food source; infestations can be large enough to weaken or damage the largest timbers, and often there is no outward sign of the larvae until the damage is extensive as the wood surface tends to remain intact; under these conditions the larval development can take between one and more than twelve years, and they have been recorded developing within damp books stored on infested shelving. Adults can find partners and mate within the timber although they will emerge on warm summer evenings to disperse by flight; here they produce characteristic round exit holes some 3-4mm in diameter along with sawdust on the timber surface. The common name refers to the adult behaviour of tapping the head against the wood surface to attract mates, they live for only six weeks or so but have a protracted emergence period and so the tapping may be heard through the spring and summer in quiet buildings. In the wild the beetle develops in a range of hardwood trees but particularly oak, willows, poplars and beech; adults are active as soon as the temperature rises in the spring and may be heard tapping through March and April. Soon after mating the females lay batches of 3-5 eggs in bark crevices or cracks in exposed timber although they often re-enter their emergence holes and move deep into the wood to oviposit. The larvae develop slowly; under ideal conditions they will be full grown during the summer and there will be a single generation each year but more generally they will take several years, the small creamy and crescent-shaped larvae are initially very active as they search for the best areas of wood
Xestobium rufovillosum 1
Xestobium rufovillosum 2
© U.Schmidt https://www.kaefer-der-welt.de/index.htm
to consume but once they begin feeding they produce galleries filled with small pellets of frass, a habit unique among the U.K. beetle fauna. Fully grown larvae excavate tunnels 3mm in diameter and eventually move to just beneath the surface to construct a pupal cell. Under ideal conditions inside all stages may occur year-round but in the wild the larvae pupate in the winter or early spring and produce adults soon after. Adults are not known to feed on wood but they do occur on umbels and other flowers and may also be found basking on areas of dead wood on stumps and trunks in bright sun, and they may occasionally be swept from foliage near suitable host material.
This is a drab brown, elongate oval and rather parallel species soon recognized by its general appearance. 5.0-9.0mm. Upper surface with coarse granules and punctures and unevenly distributed pale pubescence. Head broad and reflexed; not visible from above, with the vertex and frons broad and flat, the eyes transverse and entire, only weakly convex. Antennae filiform with all segments elongate, 9-11 much longer than the others. Pronotum campanulate, widely explanate and finely bordered; the disc is flat and the posterior margin widely sinuate, the lateral margins evenly rounded to perpendicular hind angles and rounded front angles. In fresh specimens the pubescence is dense and directed laterally and posteriorly but this soon becomes abraded and patchy. Scutellum large and densely pubescent. Elytra sub-parallel, moderately convex and flat on the disc, lacking striae but extensively punctured and granulate; the pale or golden pubescence generally forms well-defined patches in fresh specimens and is quite characteristic among our U.K. fauna. The legs are robust and pubescent throughout; pro-coxae oval and narrowly separated, the meso-coxae round and the separation a little wider, and the hind-coxae transverse and separated by the produced anterior margin of the first abdominal sternite. All tibiae are broadened towards the apex with the outer edge widely sinuate. Tarsi 5-5-5, with all segments short and robust; 3 and 4 widely bilobed on all legs. The claws are long and curved, smooth along the inside and lacking a basal tooth.