How to Identify and Treat Woodworm in Your Home

Small round holes in a skirting board, fine powder beneath a joist, a windowsill that feels softer than it should — these are the easy-to-miss signs that woodworm has moved in. The name is misleading: there’s no worm involved. Woodworm is damage left by the larvae of wood-boring beetles, and by the time you spot the exit holes, the beetle has usually already left.

I’ve checked more than a few lofts where the owner had no idea how long the problem had been there. Some infestations are long dead. Others are still active, slowly weakening a joist you’re relying on. Telling the two apart is the whole game, and it’s what this guide covers.

What Woodworm Actually Is

Woodworm is the common name for damage caused by wood-boring beetle larvae. An adult beetle lays eggs in cracks or old exit holes in timber. The eggs hatch into larvae that tunnel through the wood for one to several years, feeding as they go, before pupating near the surface and emerging as adult beetles through small round holes. That emergence hole is usually the first thing people notice — by which point the feeding damage is already done.

Untreated softwood with high moisture content is the most attractive target, which is why woodworm turns up so often in older lofts, floors, sheds and garden furniture rather than dry, modern timber.

Signs of an Active Infestation

Exit holes alone don’t tell you whether the problem is current or long finished. Look for a combination of these signs before assuming it’s active:

• Fresh, pale exit holes with sharp edges — older holes darken over time.
• Bore dust (frass) that’s fine and powdery like talc. Compacted or cobwebbed dust suggests the infestation is dormant or dead.
• Crumbly or soft timber edges when pressed with a screwdriver or thumbnail.
• Live adult beetles on windowsills, usually between May and September.
• Tunnels in cut or broken timber, often only found when a floorboard is lifted.

Which Beetles Are Usually Responsible

A handful of species account for almost every domestic case:

• Common furniture beetle — by far the most frequent culprit, targeting structural softwood and furniture alike.
• Deathwatch beetle — prefers older oak already softened by damp or decay, more common in older buildings.
• Powder post beetle — targets sapwood in certain hardwoods with a high starch content.
• House longhorn beetle — less common but capable of more serious structural damage.

For most homeowners, the exact species matters less than establishing whether the infestation is active and whether the timber is still structurally sound. A specialist can identify the species precisely if it changes the treatment approach.

How to Treat Woodworm Yourself

For a contained, confirmed-active infestation in non-structural timber, a DIY approach is often reasonable:

1. Confirm it’s active first. Don’t treat based on old, discoloured holes with no fresh frass.
2. Vacuum away loose frass and dust so you can see the extent of the holes and spot new dust later.
3. Address any damp problem. Beetles thrive in damp timber, so fixing a leak or improving ventilation matters as much as any chemical treatment.
4. Apply a permethrin or boron-based treatment fluid generously to exposed and surrounding timber, following the label’s coverage rate exactly. Use injectable fluid directly into larger, deeper holes.
5. Treat a wider area than the visible holes, since larvae tunnel beyond where a beetle emerged.
6. Monitor for fresh frass over the following year. A second treatment is sometimes needed.

When to Call a Professional

DIY treatment has real limits. Call a qualified timber and damp specialist if the affected timber is structural and shows softening or tunnelling; you suspect deathwatch beetle in older hardwood beams; the infestation covers a large area such as an entire loft; you can’t reach all the affected timber; or you’ve already treated once and are still seeing fresh frass a year on. A specialist can also carry out a structural assessment and issue a report often needed for mortgage or insurance purposes.

Preventing It Coming Back

Woodworm is fundamentally a moisture problem with a beetle attached. Keeping lofts and sub-floor voids ventilated, fixing leaks promptly, treating new timber before installation, and checking secondhand furniture for fresh holes before bringing it indoors all reduce the risk. A yearly visual check of loft timbers is a sensible habit in older properties.