Timber decay and woodworm

Can the colour of bore dust tell you a beetle attack is active?

Fresh, bright dust that reappears after it is cleared is a clue that insects are still emerging. Dust that has sat for years, or grit from the roof, is not. Colour alone is not a laboratory result, and a surveyor cannot date a handful of dust to a season just by looking.

Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.

What is the fuller explanation?

Specialists clear a patch and come back, or they look for beetles and crumbling galleries. A home survey is one visit. The surveyor should say whether dust was present and whether the timber was soft. They should not sell a spray from the colour of a pile that might have fallen out of an old hole when someone moved a box. The Property Care Association’s advice stays with moisture and the actual timber condition.

If activity matters to the price, ask for a timber inspection that will say whether the attack is current. Do that before you budget a chemical treatment of every joist. Costs vary. Historic holes in dry sapwood often need no chemical at all, which is a conclusion for the specialist, not a slogan for the seller.

What should you ask your surveyor?

Did fresh dust reappear, or did you see a single old deposit?
Was the surrounding timber firm or crumbly?
Are you recommending treatment, or only recording evidence that should be checked?

What are the typical next steps?

Do not vacuum the dust away before a specialist visit if you need it as evidence.
Do not accept a spray quote written from the survey’s adjective.
Ask the specialist to separate active attack, historic holes and wet rot in the same timber.

Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.

Also asked about this

Is frass the same as dust from plaster?

Frass is the bore dust insects leave. Plaster grit is not frass. They can sit in the same loft. Ask which the surveyor means.

Does one beetle on the window board mean the rafters are infested?

It means a beetle was there. It does not map the roof. Ask for the timbers to be looked at if the survey has raised it.