Signs of Woodworm: How to Spot an Active Infestation

Woodworm rarely announces itself. The beetle responsible spends three to four years quietly tunnelling inside the wood, and by the time you notice anything on the surface the infestation may have been at work for several seasons. Knowing what to look for, and being able to tell a live infestation from old damage that stopped years ago, can save you both worry and money.

This guide runs through the main signs of woodworm, what each one tells you, and the simple checks that separate an active problem from a historic one.

What woodworm actually is

“Woodworm” is not a worm at all. It is the larval stage of several wood-boring beetles. The grubs hatch from eggs laid in bare timber, eat their way through the wood for years, and finally chew their way out as adult beetles in late spring and summer. The damage you can see is mostly the holes left behind as the adults emerge.

The species you are most likely to meet is the common furniture beetle (Anobium punctatum), which causes around three quarters of UK infestations and leaves 1 to 2mm round holes. Less common but more serious are the death watch beetle (Xestobium rufovillosum), found in old oak with 3mm holes, and the rare house longhorn beetle (Hylotrupes bajulus), with large 6 to 10mm oval holes. Identifying the culprit matters, because the treatment and urgency differ. Our common furniture beetle guide covers the most frequent offender in full, and the Property Care Association sets the industry standards that qualified timber surveyors work to.

The seven signs of woodworm

1. Exit holes

The classic sign is a scatter of small round holes in timber, each roughly the diameter of a pencil tip or smaller. For the common furniture beetle these are 1 to 2mm across with clean, circular edges. Holes appear on floorboards, joists, skirting, roof timbers, staircases and wooden furniture. On their own they only prove a beetle once left, not that anything is still inside, so they are the start of the investigation rather than the conclusion.

2. Frass (bore dust)

Frass is the fine, gritty powder the larvae push out of the timber as they tunnel. It looks like sawdust or fine sand and collects in small heaps below or beside infested wood, on skirting, in the angles of joists or on the floor of a loft. Fresh frass is the single most useful sign of an active infestation: it is clean and the colour of the surrounding timber, and it keeps reappearing after you brush it away.

3. Tunnels and galleries

Behind the surface, the larvae carve a network of tunnels, sometimes called galleries, that run with the grain. You usually only see these where timber has split, broken or been cut, revealing a honeycombed interior packed with frass. Extensive tunnelling is a sign the infestation has been working for some time and may have weakened the wood.

4. Weak, crumbling or damaged timber

As the galleries multiply, the timber loses strength. Warning signs include:

• Edges of joists, beams or floorboards that crumble or flake away.
• A screwdriver or bradawl blade that pushes easily into wood that should be firm.
• Floors that feel springy or bounce underfoot.
• Visibly sagging joists, rafters or wall plates.

Structural weakness of this kind is the point at which woodworm stops being a cosmetic nuisance and becomes a safety matter, and it usually warrants a professional survey rather than DIY.

5. Live beetles

Adult beetles emerge mainly between May and September. Common furniture beetles are small, 3 to 5mm long, reddish-brown to dark brown, with a slightly hunched back. You may find them on or near affected timber, on windowsills, or drawn to windows as they try to leave. Live adults in season are strong evidence of a current, breeding infestation.

6. Dead beetles

Even when you do not catch the adults alive, you may find their bodies. Look on windowsills, in light fittings, on the floor beneath roof timbers, or caught in cobwebs near infested wood. A cluster of recently dead beetles suggests a generation emerged in the last season or two.

7. Eggs and bored timber edges

Less obvious but worth checking: females lay tiny, pearl-coloured eggs in cracks, crevices and existing holes in bare timber. You are unlikely to spot the eggs themselves with the naked eye, but rough, “bored” end grain and crevices full of fresh dust on unpolished timber point to recent egg-laying and emergence.

Where woodworm is most often found

Knowing where to look is half the battle, because the beetle favours timber that is cool, undisturbed and slightly damp. The places worth checking first in a typical UK home are:

• Suspended timber floors. The undersides of floorboards and the joists beneath them, especially near external walls and over poorly ventilated voids, are classic hotspots. Lift a board at the edge of a room and look at the joists with a torch.
• Roof spaces. Rafters, purlins and the wall plates where the roof meets the masonry collect dust and moisture and are a frequent site of infestation. Bring a torch and check the timber where it sits on the walls.
• Cellars and sub-floor areas. Cool, humid and rarely inspected, these spaces suit egg-laying beetles well.
• Staircases and skirting. Unpolished or hidden faces of stair strings, treads and skirting boards are easy to overlook.
• Wooden furniture and reclaimed timber. Antiques, chests, drawer bottoms, picture frames and second-hand timber are a common way infestations enter a house in the first place. Always check the backs and undersides where the wood is bare.

Older properties, those with original softwood joists and rafters, and homes with any history of damp are the most likely to be affected. Newer timber is often pre-treated and far less vulnerable.

When do the beetles emerge?

Timing matters when you are trying to confirm an infestation. Adult common furniture beetles emerge and fly mainly between May and September, with the peak in early summer. This is when you are most likely to see live beetles, find fresh exit holes appearing and notice new frass. If you inspect in the depths of winter and find no beetles, that does not prove the infestation is dead, only that the adults are not active yet. The reliable test is to clear the dust, mark the holes, and re-check during the emergence season.

Active or historic? How to tell the difference

This is the question that decides whether you need to spend anything at all. A great many properties carry old woodworm damage from an infestation that died out decades ago, often because the timber dried out and became inhospitable. Treating dead damage is wasted money, so it pays to check carefully.

Signs the infestation is active:

• Fresh, pale frass that matches the timber colour and reappears after cleaning.
• Holes with sharp, clean, light-coloured edges.
• Live or freshly dead beetles in spring and summer.
• Timber that is, or recently was, damp.

Signs the damage is historic:

• Holes with dull, darkened, weathered edges, sometimes with old paint or polish over them.
• Grey, compacted dust that does not return once removed.
• No beetles, no fresh frass and dry, stable timber.

A reliable home test is to vacuum away all visible dust, seal the holes lightly with a thin layer of decorator’s filler or mark them with a pencil, and re-inspect after a few weeks during the emergence season. New holes or new frass confirm live activity. Our dedicated guide to active vs historic woodworm explains the surveyor’s methods in more depth, including the moisture and timing checks they rely on.

What to do if you suspect woodworm

If your checks point to an active infestation, the sensible steps are:

1. Identify the species if you can, since this affects urgency and method.
2. Assess the extent, noting whether timber feels weak or the damage looks structural.
3. Look for damp, as moisture is what allows most infestations to take hold.
4. Decide on treatment. Limited surface infestation by the common furniture beetle can sometimes be tackled with a DIY permethrin or boron product, while structural damage, uncertain identification or roof timbers call for a professional. Our how to treat woodworm guide walks through both routes in full.

If you are unsure whether what you have found is active, getting a qualified eye on it removes the guesswork before you spend a penny on chemicals or repairs.

Get professional help

Not sure whether those holes are old damage or a live problem? A free survey from a qualified specialist will confirm whether the woodworm is active, identify the beetle and tell you exactly what, if anything, needs doing. Get a free quote today and put your mind at rest with a clear, written assessment.