Woodworm: signs, treatment and whether it is still active
The signs of woodworm, how to tell old holes from an active infestation, what causes it, DIY against specialist treatment, bats in the loft, and buying a house with woodworm.
Woodworm is the larva of a wood-boring beetle, and the small holes in a floorboard, a joist or an old chest of drawers are where adult beetles chewed their way out. Some holes are from beetles long gone, and some mean larvae are still feeding. We cover the signs, how to tell whether woodworm is still active, what causes it, DIY against specialist treatment, and buying or selling a house with it.
What woodworm is
Woodworm is not one insect but the larval stage of several wood-boring beetles. The female lays eggs in cracks and old holes in the timber surface, the eggs hatch within three weeks, and the larvae tunnel through the wood for 2 to 5 years. Each then pupates, and the adult beetle chews its way out, so the exit holes mark the end of the damage, not the start.
The woodworm beetles found in UK homes
The common furniture beetle causes around 75% of UK woodworm cases, and the other four turn up less often.
| Beetle | Scientific name | What to know |
|---|---|---|
| Common furniture beetle | Anobium punctatum | Around 75% of UK woodworm cases |
| Death watch beetle | Xestobium rufovillosum | Historic buildings, in hardwood already softened by fungal decay |
| House longhorn beetle | Hylotrupes bajulus | Found in the UK mostly in the South East |
| Wood boring weevil | Euophryum confine | Exit holes around 1mm across, linked to wet rot |
| Powder post beetle | Lyctus brunneus | Wide-pored hardwoods such as oak, ash, sycamore and walnut |
Signs of woodworm
Woodworm usually shows first as a patch of small holes in floorboards, loft timbers, stair treads or the back of an old piece of furniture. The timber around the holes tells you whether the beetles are long gone or still at work.
| Sign | What to look for | What it tells you |
|---|---|---|
| Exit holes | Small holes, most around 2mm across | Adult beetles have emerged; clean, sharp edges mean the holes are fresh |
| Frass (bore dust) | Dust like very fine sawdust below the holes | Larva droppings; fresh dust means larvae are still feeding |
| Adult beetles | Live beetles on or near the timber, May to October | An active infestation |
| Damaged floorboards | Boards that feel weak, with crumbly edges | Damage under the surface; check the joists too |
Woodworm in floorboards
Floorboards show woodworm as clusters of holes and as boards that feel weak underfoot, with edges that crumble when pressed. The joists under them carry the floor, so lift one board where the damage is worst and check the joist tops before deciding who treats it.
How to tell if woodworm is still active
Fresh holes with clean edges, new dust and live beetles between May and October mean it is still active. Holes with no dust below them and no new holes over a full summer point to an infestation that has died out, and holes like that need no insecticide, because there is nothing left to kill. The only question then is whether the timber is still sound.
The larvae feed all year, but nothing new appears on the surface until the adults emerge from May, so a beam that looks quiet in January proves little.
What causes woodworm
Beetles arrive in timber already carrying eggs or larvae: second-hand and antique furniture, wicker baskets, old timber boxes and firewood are the usual ways in. Emerging adults then mate and lay eggs on other timber nearby, which is how one infested chair becomes a problem in the floor.
Damp makes it worse. Woodworm beetles prefer wood that has been damp, the wood boring weevil is linked to wet rot, and the death watch beetle to hardwood softened by fungal decay. Woodworm in a loft or under a ground floor often has a moisture problem beside it, from a leaking roof, blocked airbricks or damp and condensation, and that needs fixing alongside the treatment.
Timber that is soft or crumbling with no exit holes points to rot rather than beetles. Wet rot and dry rot are fungal decay, an insecticide does nothing for either, and a timber survey looks for both.
Is woodworm serious?
Woodworm is not directly harmful to people, and you can live in a house with it while it is dealt with. It is very rarely severe enough to weaken a structure.
The exception is timber that carries weight. Some beetles left untreated can cause serious structural damage, so active woodworm in joists, rafters, a beam or a staircase gets a specialist look even when the furniture is fine.
Woodworm treatment: DIY or a specialist
An insecticide applied to the timber kills woodworm and in most cases clears the infestation. Sound timber is treated, and timber too weak to do its job is cut out and replaced.
| Situation | Who treats it | Why |
|---|---|---|
| A chair, chest or picture frame | DIY woodworm killer | Small, loose and reachable from every side |
| A few holes in one or two sound floorboards | DIY, or a specialist if the joists are affected | Lift a board and look at the joists first |
| Joists, rafters, beams or a whole floor | Specialist | Load-bearing timber, where a survey decides what to treat and what to replace |
| A loft with signs of bats | Specialist, after the bat helpline | No chemicals near a known roost while bats are present |
DIY woodworm killer is a brush-on fluid sold at DIY stores and timber merchants, with no guarantee.
Woodworm in joists, rafters and floorboards is work for damp and timber specialists, since damp proofing firms also treat timber and look for the damp behind it.
Ask which product will be used and check it is an HSE-approved formula. The treatment should come with a written, long-term guarantee, and some specialists give 30 years, backed by guarantee protection insurance so the cover outlasts the firm.
Like other specialist damp and timber treatment, woodworm work is priced after a survey, on the area of timber treated, how many boards come up to reach the joists and whether any timber is replaced.
Treating woodworm in a loft with bats
Bats roost in roof spaces, and in England all bat species, their breeding sites and resting places are fully protected by law. The government's guidance on timber treatments near bat roosts says you cannot use chemical products in or near a known roost while bats are present.
Search the loft for signs such as fresh droppings before any treatment starts. Householders should call the bat advice helpline, which is free for them, before using a chemical product near a roost, and treatment is usually best done between autumn and spring. These rules apply in England.
Buying or selling a house with woodworm
In England, woodworm usually comes to light in the buyer's pre-purchase survey. Found that way, it is normally a treatment job rather than a reason to pull out. Get a written quote for the treatment and any timber replacement, then negotiate on the price or ask the seller to have the work done before completion.
Scotland works differently. The seller or selling agent must give a buyer a Home Report within 9 days of being asked. It contains a single survey covering the home's condition and any repairs needed, and a property questionnaire that covers past damage and guarantees, which is where an earlier woodworm treatment would show.
If you are selling a treated house, have the specialist's report and guarantee ready before it goes on the market, because a buyer's surveyor who spots old exit holes will ask for both.
How to prevent woodworm
- Check before it comes indoors. Look over second-hand furniture, wicker baskets, old boxes and firewood for holes and dust.
- Keep timber dry. Clear the airbricks, ventilate the loft and fix leaks.
- Seal bare furniture. A varnish made to protect timber furniture helps stop woodworm taking hold.
- Look again each summer. New holes appear from May to October, so check the loft and old furniture then.
Common questions
Can you get rid of woodworm?
Woodworm can be got rid of: an insecticide applied to the timber kills the larvae and clears the infestation in most cases. Sound timber is treated, and timber too weak to do its job is cut out and replaced. Fixing the damp that attracted the beetles stops them coming back.
Can you live in a house with woodworm?
You can live in a house with woodworm, because it is not directly harmful to people. It is very rarely severe enough to weaken a structure, though some beetles left untreated can seriously damage load-bearing timber. Have active woodworm in joists, rafters or beams checked by a specialist.
What time of year is woodworm active?
Adult woodworm beetles emerge between May and October, which is when new exit holes and fresh dust appear. The larvae feed inside the timber all year round for 2 to 5 years before that. A beam that looks quiet in winter can still have larvae inside it.
How do you tell if you have woodworm?
Look for small holes around 2mm across, dust like fine sawdust below them, weak floorboards with crumbly edges and live beetles from May to October. Fresh holes with clean edges mean the woodworm is still active. No new dust and no new holes over a summer point to an old infestation.
Should I buy a house with woodworm?
A house with woodworm is usually still worth buying once a specialist has confirmed which beetle it is, whether it is active and what the treatment involves. Get the treatment quoted in writing before exchange and use it to negotiate on the price.