The Wood Guide · Calculating with wood
Practical guideSmall holes in an old cupboard, fine white powder on the windowsill below a beam. Woodworm works quietly but effectively — and if you do nothing, you risk structural damage.
Before you treat anything, you need to know whether there is still life in it. Woodworm is the larva of a wood-boring beetle — in our part of Europe usually Anobium punctatum, the common furniture beetle. The larvae tunnel through the wood for years before emerging as beetles, typically from May to August.
Round holes one to two millimetres across — the most visible sign, but they tell you nothing about whether it is still active.
Fine, pale powder under or beside the wood points to recent activity. Old, caked frass means an old, possibly inactive infestation.
Tap the surface with your knuckle or a hammer. A hollow sound indicates tunnels eaten out inside.
In spring, lay a sheet of white paper under the suspect piece of furniture or beam. Fresh frass falling onto it confirms active woodworm. This is the most reliable test.
| Material or tool | What for |
|---|---|
| Woodworm treatment (liquid or spray) | Chemical treatment of affected areas |
| Injection syringe or injector bottle | Getting the treatment straight into the holes |
| Wide brush or roller | Surface treatment of larger areas |
| Plastic sheeting or dust sheet | Sealing treated wood for better penetration |
| Disposable gloves and safety glasses | Personal protection when using chemicals |
| Dust mask (P2 or higher) | Protection against fumes and wood dust |
| Heat gun or infrared lamp | Heat treatment without chemicals |
| Non-contact thermometer | Monitoring temperature during heat treatment |
Products based on permethrin or boric acid penetrate deep into the wood and kill larvae at every stage. This is the usual route for beams, floors and furniture you cannot heat or move.
Always work in a well-ventilated room, wear gloves, glasses and a dust mask, and keep the product out of reach of children and pets.
Larvae die at a core temperature of 55 °C held for at least sixty minutes. Ideal for antique or lacquered furniture where chemicals would damage the surface.
Put the piece in a closed, heated room or use a professional heat chamber. Mobile units can be hired from specialist companies.
A heat gun or infrared lamp can be used locally, but without a thermometer it is hard to guarantee the core temperature deep inside the wood.
Surface temperature is not the same as core temperature. With thick timber it takes much longer for the core to heat up — measure it, don't guess.
Figurines, small pieces of furniture and bookends can simply go in the freezer.
Wrap the object airtight in plastic film and leave it in a freezer at -18 °C or colder for at least two weeks. Woodworm larvae do not survive that cold. Note: condensation during thawing can damage the wood — let it come up to room temperature slowly.
| Method | Best for | Advantages | Drawbacks |
|---|---|---|---|
| Chemical treatment | Beams, floors, large furniture | Thorough, also works preventively, widely available | Chemical exposure, needs good ventilation |
| Heat treatment | Antique or delicate furniture | No chemicals, no residue | Expensive equipment, difficult on large structures |
| Cold treatment | Small wooden objects | Simple, can be done at home | Small pieces only, risk of moisture damage when thawing |
| Professional fumigation | Severe, widespread infestations | Most complete result | High cost, building must be vacated temporarily |
The same pest, three very different approaches.
Situation: in June the owner finds fresh frass and new exit holes in a nineteenth-century cupboard.
Approach: every hole injected with a permethrin solution, then the entire surface brushed — including the inside and the back panel. Covered with plastic for five days, a second treatment four weeks later. After three months, no more signs of activity.
Situation: extensive infestation in oak roof beams, with frass spread over several metres.
Approach: a professional firm called in for a combined approach — chemical injection of all the beams, followed by a preventive surface treatment. An annual inspection set up.
Situation: woodworm in a collection of small devotional figurines, where chemical treatment would damage the paintwork.
Approach: each object wrapped individually in plastic and frozen for three weeks at -20 °C. After slow thawing, no new activity found.
Woodworm prefers damp, untreated wood. A dry, well-ventilated environment is the best protection there is.
Keep the humidity in crawl spaces and lofts below 60%. Without damp wood, the larva struggles.
Treat unlacquered or untreated wood every year with a preventive product, ideally in early spring — before the flight season begins.
Check every second-hand piece thoroughly before you bring it indoors. One infested object can spread to a whole interior.
Look over floor joists, roof trusses and furniture at least once a year, ideally after the flight season, in September or October.
Solid hardwood such as teak or meranti is denser and oilier than home-grown softwood, which makes it less attractive to larvae. Invest in quality hardwood garden furniture and you get that advantage built in.
Lay a sheet of white paper under the suspect piece in spring. Fresh, pale frass falling onto it proves active larvae. Old, caked frass points to an old infestation that may already have stopped.
Typically from May to August. That is why you are best off checking after the flight season, in September or October, and treating preventively in early spring.
Yes. Larvae die at a core temperature of 55 °C held for at least sixty minutes, or after two weeks of freezing at -18 °C. Both work, but with thick timber the core temperature is hard to guarantee — measure it with a non-contact thermometer.
Keep the wood dry: below 60% humidity the larva does not survive well. Inspect second-hand furniture before it comes indoors, and give untreated wood a preventive treatment every year in early spring.
For load-bearing structures — roof trusses, floor joists — or when the infestation extends over several metres. Structural safety is not DIY territory.
Woodworm is one of the things you prevent with good maintenance. The rest is in our guides.
Unsure about your situation? Ask your question — we're happy to take a look.
The Wood Guide
Other sections:Wood speciesCare & finishingChoosing & buyingBuild it yourselfTrees & forests
