Woodworm is the larvae of wood-boring beetles, and the usual sign is small round exit holes in timber. Many infestations are old and no longer active; fresh, pale holes and fine bore dust (frass) suggest activity. Treatment is only needed for active infestations, and reducing moisture in the timber is a big part of control.
Woodworm is one of those things that panics people on a pre-purchase survey. A few holes in a floorboard or loft timber and suddenly they think the house is being eaten. Most of the time, it isn’t.
What woodworm is
It’s the larvae of wood-boring beetles. In most UK homes it’s the common furniture beetle. The adult lays eggs in cracks in the timber, the larvae tunnel through the wood for a few years, then emerge as adults through small round exit holes. Death watch beetle and house longhorn beetle exist too, but are much less common and found in particular situations, such as old hardwood structures or certain areas.
Active or historic?
This is the big question. Lots of houses have old woodworm holes from an infestation that died out long ago.
- Signs of activity: clean, sharp-edged holes with fresh, pale wood inside; fine, gritty bore dust, called frass, under holes or on surfaces below; and holes appearing in timber that’s been recently cleaned or painted.
- Signs it’s historic: holes that are dark inside and the same colour as the surface, with dust that is old, compacted or covered in dirt or cobwebs.
If you’re not sure, you can mark or seal the existing holes, or put a sheet of dark paper under the area, and check next spring and summer, when adult beetles emerge, for new holes or fresh dust.
Moisture is the key
Common furniture beetle prefers damper timber. Dry timber in a heated, well-ventilated house is much less attractive. That’s why I tend to find activity in damp cellars, subfloors, under stairs and in poorly ventilated lofts and outbuildings rather than in warm, dry rooms.
Treatment
- Where activity is confirmed, fix any damp first and improve ventilation.
- Timber that’s been weakened needs assessing and, if necessary, replacing or strengthening.
- An insecticidal treatment, applied by a competent contractor to the affected timbers, may be recommended where there is active infestation.
What I don’t agree with is whole-house chemical spraying just because a few old holes were spotted. Diagnose first, treat what needs treating.
When to call a specialist
If you've found woodworm holes and aren't sure whether they're active, a timber survey will confirm it and tell you whether treatment is actually needed. Book a survey with All Dry on 01226 287181 or email info@alldrydampproofing.com.
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Frequently asked questions
What does active woodworm look like?
Clean, pale exit holes and fresh, fine bore dust beneath them.
Do old woodworm holes need treating?
Not if the infestation is no longer active, though weakened timber should be assessed.
Does damp cause woodworm?
Damp timber is more attractive to common furniture beetle, so reducing moisture helps control it.