|Building Conservation: Wood-Boring Insects|
A number of insects cause decay of timber in our buildings. The best known are Anobium punctatum (woodworm) and Xestobium rufovillosum (Death watch beetle). They lay their eggs on the surface of the wood, the hatching larvae tunnel in the timber and create galleries. The tunnelling causes structural damage to the timber.
Often the insects' activities are not significant, as the timber species may dictate that only the sapwood is consumed, which may only be a small cross-section of, for instance, a floor joist. The adult insects can be seen on the timbers during the flight season (April to August) and dust (frass) may be seen on the floor beneath infected timbers as the insects emerged from the wood.
Most buildings surveyed will have extinct infestations. These do not need treatment; however, inexperienced surveyors and parties with vested interests will recommend chemical treatments. This often means that extinct outbreaks have been treated many times, particularly if a house has changed hands often in the last thirty years.
If an active infestation is found then the circumstances surrounding the attack need to be considered carefully. For instance, does the timber have high sapwood content, what species of timber is it, how wet is the timber, what would be the cost of replacement rather than treatment? More often than not infestations only require changes in the environmental conditions to reduce the moisture content of the wood, for instance, increasing ventilation to a roof void. The infestation will eventually die out as the timbers dry.
Rarely, some targeted chemical treatments and monitoring may be needed. Beware of someone recommending complete insecticide treatment of all timbers in a building, as this is unnecessary, does not address underlying causes, and kills natural predators of the insects.
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