Woodworm is one of the most common findings in older UK houses, and one of the most commonly over-treated. Small round holes in a floorboard or joist don’t automatically mean you need treatment. Often the beetles that made them died out years ago. Here’s how to tell whether you have an active problem, and what actually needs doing.
What woodworm is
“Woodworm” isn’t a worm. It’s the larvae of several wood-boring beetles. Adults lay eggs in cracks in timber, the larvae tunnel through the wood for years, feeding on it, and then emerge as adults through small exit holes — the round holes most people recognise.
The damage is done by the larvae inside the timber, which is why the holes you can see are only part of the story.
What woodworm looks like
- Small round exit holes in timber, typically 1–2 mm across for the most common beetle.
- Fine, powdery dust called frass, gritty like sawdust, around the holes or on the floor below.
- Crumbly edges to boards, joists or skirtings where the tunnelling is heavy.
- Adult beetles emerging or dead near window sills in spring and summer.
- Weak or damaged floorboards or joists in severe, long-standing cases.
The Property Care Association’s guide to the signs of woodworm has photographs of each.
Active or historic? The question that matters
Most woodworm found in surveys is historic — old holes from an infestation that has already died out. Treating historic woodworm achieves nothing. Signs that an infestation is active:
- Fresh frass: light-coloured, crisp dust, especially if it reappears after you clean it up.
- Clean, sharp-edged holes with bright wood inside, rather than dark, dusty, weathered ones.
- Adult beetles emerging, typically in spring and summer.
- New holes appearing over a season.
A simple test is to clean an area thoroughly, or put a sheet of dark paper beneath suspect timber, and check again after the emergence season. No new frass and no new holes usually means no active infestation.
The common beetles
- Common furniture beetle — by far the most common in UK homes, attacking softwood and some hardwoods, with exit holes around 1–2 mm.
- Death watch beetle — larger holes, around 3 mm, mostly in old hardwood, particularly oak, that already has fungal decay. Usually found in historic buildings.
- House longhorn beetle — larger, oval exit holes, and a serious pest of softwood roof timbers, but in the UK largely confined to parts of Surrey.
- Wood-boring weevils — found in timber that is already decaying from damp, which makes the damp the real problem.
Identifying the beetle matters, because it tells you how serious the risk is and what’s driving it. The PCA’s guide to woodworm beetles covers them in more detail.
Why damp and woodworm go together
Wood-boring beetles thrive in timber with a higher moisture content. In a modern, dry, centrally heated home, many infestations struggle and die out on their own. Where there is active woodworm, there is often a moisture problem too: a damp subfloor with blocked airbricks, a leaking roof, or timbers in contact with a damp wall. Fixing the damp is often the most effective long-term woodworm control, and it’s essential where weevils or death watch beetle are involved, because they depend on decaying, damp wood.
When woodworm treatment is needed
Treatment makes sense when there is evidence of active infestation in timbers that matter — structural floor joists, roof timbers, staircases. In that case:
- Identify the beetle and confirm activity.
- Deal with any damp driving it.
- Treat only the affected timbers, with a suitable product applied by a competent contractor.
- Replace timber that is structurally weakened.
When it isn’t
Treatment is not needed for:
- Historic holes with no sign of recent activity.
- Infestations in timber that is dry and staying dry, where the beetles are likely to die out.
- Blanket treatment “as a precaution” across a whole house, which is sometimes sold alongside other work.
A woodworm guarantee is only worth having if the treatment was needed in the first place.
Buying a house with woodworm
Woodworm is common in older houses and rarely a reason to walk away. What you need before exchange is to know whether it’s active, whether it has weakened anything structural, and whether there’s a damp problem behind it. A Home Survey Level 3 will flag signs of woodworm and decay. Where treatment has been recommended, or you want certainty, an independent damp and timber survey confirms whether the infestation is active and whether any work is genuinely needed — and because we sell no treatment, our only interest is the right answer.
Related: dry rot vs wet rot · what rising damp really is · our damp checker.
Sources and further reading
- Signs of woodworm — Property Care Association
- Woodworm beetles: types and signs — Property Care Association
- Homeowner advice hub — Property Care Association