Identify and compare
Woodworm or not? Holes in wood compared
Not every hole in wood is woodworm, and not all woodworm is active. The key sign of a live infestation is fresh frass, a fine biscuit-coloured dust falling from clean, pale-edged exit holes. Old grey holes with no frass usually mean a long-dead infestation. Nail holes, screw holes and knots are not woodworm at all.
Woodworm worries people because of the structural risk, but the Property Care Association notes that not all woodworm is active and not all active woodworm needs the same response. Working out whether the holes are live, dormant or not woodworm at all comes first.
Use the table to compare what you are seeing, then read how to confirm activity. For structural timber or signs of the rarer beetles, get a specialist assessment.
At a glance comparison
| What you see | Likely cause | Active? | What it means | |
|---|---|---|---|---|
| Clean holes plus fresh dust | Round 1 to 2mm holes, pale inside, with gritty biscuit-coloured frass below | Active common furniture beetle (woodworm) | Yes | A live infestation; identify the beetle and assess, treat where needed |
| Old grey holes, no dust | Round holes that look weathered or grey, no fresh frass | Long-dead woodworm | No | Usually historic and inactive; monitor rather than treat reflexively |
| Larger or oval holes | Holes larger than 2mm or oval, sometimes with bun-shaped frass | Possible deathwatch or house longhorn beetle | Maybe | The rarer, more serious beetles; get a specialist assessment |
| Regular holes in a line | Evenly spaced or paired holes, no frass, often with a fastener nearby | Old nail or screw holes, or fixings | No | Not woodworm; mechanical, not biological |
How to tell them apart
Frass is the deciding sign
The single most reliable test for an active infestation is frass: a fine, gritty, biscuit-coloured dust that falls from the holes onto surfaces below. Fresh frass means beetles are still emerging. Wipe a surface clean, leave it, and check again over the spring and summer flight season for new dust.
Look at the holes themselves
Active common furniture beetle leaves round holes about 1 to 2mm across that look clean and pale inside. Old, long-dead holes look grey and weathered with no fresh dust. Holes larger than 2mm, or oval rather than round, can point to the rarer deathwatch or house longhorn beetle.
Rule out things that are not woodworm
Evenly spaced or paired holes, especially near a fixing, are usually old nail or screw holes. Knots and natural timber features are not beetle damage either. None of these produce frass, which is why the dust test is so useful.
Frequently asked questions
How do I know if woodworm is active?
The clearest sign is fresh frass, a fine biscuit-coloured dust falling from clean, pale-edged exit holes. Wipe the surface clean and check again through spring and summer; new dust means a live infestation. Old grey holes with no fresh frass usually indicate a long-dead, inactive infestation.
Are all holes in old wood woodworm?
No. Nail holes, screw holes, knots and mechanical damage are often mistaken for woodworm. Real woodworm exit holes are round, roughly 1 to 2mm across for the common furniture beetle, and an active one produces frass. Evenly spaced holes near a fixing are almost always old fastenings.
Does old woodworm need treating?
Not necessarily. The Property Care Association notes that not all woodworm is active and not all active woodworm needs the same response. Long-dead, inactive holes in sound timber often just need monitoring. Active infestation, or any sign of the rarer beetles in structural timber, warrants a specialist assessment.
Which woodworm beetles are the serious ones?
The common furniture beetle is usually manageable. The deathwatch beetle and house longhorn beetle are rarer but can seriously weaken structural timber such as floors and roofs, and tend to leave larger holes. Suspected signs of either should be assessed by a timber specialist.
Sources
Editor, HomesAndHedge
Oliver leads HomesAndHedge's editorial coverage of home and garden problems. He researches and writes the plain-English explainers on pests, invasive plants, damp and mould, drainage and wildlife, drawing on guidance from bodies such as the Property Care Association, the RHS and the NHS, and is clear about when a job needs a qualified professional.
Last reviewed: 8 June 2026