A medium-sized wood-boring beetle (scientific name Xestobium rufovillosum), Death Watch beetle is a notorious pest as larvae can cause major damage to wood beams and floors in buildings and to wooden furniture.
The death watch beetle is common and widespread in southern England, but less common in the North.
The adult females lay eggs in crevices or holes in dead wood, especially the hardwoods such as oak or elm often used as structural timbers in traditional buildings. The eggs hatch into larvae, which then tunnel into the wood. it is these larvae that do most of the structural damage to the wood.
The presence of the larvae in wood can go unnoticed until the adults emerge, leaving distinctive holes at the surface. These exit holes measure around three to four millimetres in diameter, considerably larger than those left by the common furniture beetle (Anobium punctatum).
During their mating season the beetles bang their heads against the wood, creating a distinctive tapping or ticking sound. It is likely that the ‘Death Watch’ name derives from people hearing this sound during the quiet of the night while they were keeping watch over a dying or dead person in an old house or church. A superstition grew that anyone hearing the sound would soon die.
Death Watch beetle prefers damp conditions especially when there has been some kind of fungal decay such as wet rot in the timbers.
A building survey will indicate if there is visible evidence of Death Watch Beetle, such as flight holes and tunnels. As damage is most likely to be found in period properties a specialist survey is recommended for purchasers of such properties unless there is evidence that previous attacks have been eradicated and remedial treatment carried out.
The larvae tend to tunnel towards the centre of the timber resulting in damage that may be more extensive than is apparent from the exterior. The structural integrity of the timber should always be checked if there is evidence of an attack. New diagnostic techniques, using a combination of ultrasound and micro-drilling, allow very precise location of cavities and tunnels within the cross-section of the timber.
It can be difficult to determine whether a beetle attack is active or dead, and whether treatment is necessary. Death Watch Beetle attacks found in historic buildings may have died out many years – even centuries – ago, but the distinctive flight holes will still be evident.
The presence of fresh, brightly coloured bore dust and clean dust-free flight holes certainly indicates that the attack is active, but their absence may not necessarily mean that the attack is dead. The larvae can remain inactive but viable for many years if conditions are unfavourable, only to re-emerge later.
Treatment may include:
- Chemical treatment to kill off beetles and larvae
- Removing and replacing badly decayed timber
- Taking steps to ensure timbers do not remain in contact with any source of damp, e.g. where existing roof timbers are laid directly on solid stone or brick walls