Xestobium squalidum LeConte 1874 , Anobium tessellatum Olivier 1790
Grande vrillette ; Vrillette marquetée ; Vrillette damier ; Horloge de la mort 
Death watch beetle 
El escarabajo del reloj de la muerte 
Der bunte Klopfkäfer ; Gescheckte Nagekäfer ; Bunte Pochkäfer The Xestobium genus comprises 4 species in France, among which death watch beetles, the biggest Anobiidae species in France.
Their feeding diet is strictly xylophagous. They are particularly dreaded in museums and libraries where they mostly infest old wood panelling, old floorings, roof timbers, staircases…
They preferably infest dead wood previously infested by lignin-degrading fungi. Death watch beetles are very common in urban areas, but they are also found in natural environments where they develop in old tree stumps and decomposing tree trunks.
The popular name “death watch beetle” originates from the fact that at night, when males are seeking females, they regularly bump their head in galleries and thus produce a sound like the ticking of a clock.
5 to 8 mm long.
Oval, elongate, sturdy. Big, wide thorax that partly covers the head.
Fairly short antennae composed of 11 articles; the last 3 articles form a barely developed club.
Dorsal faces of thorax and elytra are finely grainy, with irregular tufts of short, bent, golden bristles that give them a characteristic mottled aspect.
Reddish brown
10 to 11 mm long at the end of their development.
Look like small white grubs, sharply arched at their rear end.
Short, abundant hairiness on the whole body.
3 or 4 rows of spinules are visible on the dorsal face of the metathorax and of the first 7 abdominal segments.
Milky (sometimes pinkish) white, with black mouthparts.
It is at least 2 years long, 3 years on an average, and can exceptionally last up to 10 years. The species is heliophilic. It is frequently seen nearby windows in spring. Mating can occur as soon as imagoes come out and usually takes place outside galleries.
The eggs (60 to about one hundred on an average) are laid in small bunches, preferably in cracks and in the former galleries of the infested substrate. They are egg-shaped, 0.6 to 0.7 mm long, opaque white, and their utter surface is smooth. The incubation period lasts about 2 weeks. As soon as they have hatched, new-born larvae immediately infest their food substrate by boring galleries. Galleries are bored in all directions of the wood grain.
Several larval molts take place before nymphosis. Once they are formed, imagoes can stay in nymphal cells until winter is over and do not take flight before April. Adults’ emergence holes (or exit holes) are round, and 2 to 4 mm in diameter. Bore-dust (a mixture of substrate and larval faeces) is highly characteristic. It is formed of small, brown lentils, about 1 mm in diameter.
These insects develop in woods previously infested by lignin-degrading fungi, and the nutrients needed for their larvae are provided from the nitrogen released by the fungi (the causal agents of dry rot or white rot). Thermo-hygrometric conditions are therefore doubly important, and a minimum temperature of 22 to 25°C is required, together with a 22% humidity rate in the wood.
Adults live about 8 to 10 weeks, sometimes much longer.
In normal biotic and abiotic conditions, there is one generation every two years. That time can be lengthened or shortened depending on environmental factors (the thermo-hygrometric factor and the nutritive quality of the wood).
Xestobium rufovillosum cause most important damage to old timber woods, wood-panelling, floorings, parquet floors and any woodwork (old furniture, sculptures, paintwork frames and works of art) made from the soft part of woods from deciduous trees.
Wood panelling in very old buildings (churches, chapels, castles…) are quite often infested by death watch beetles due to the high humidity rate often found in these places.
The wood species they are most attracted to, and therefore the most susceptible ones, are oak, birch, alder, elm, willow.
Death watch beetles are rarely found in modern houses and buildings as the humidity rate in these places is too low, but they very often infest old buildings.
An increase in infestations by that species has been recorded following some special climatic events (heavy rains, floods, cyclones…).
Xestobium rufovillosum are widely distributed in Europe. They are also found in North America and Australia.
