Woodworm is the name often given to the larvae of wood-boring beetles. Many holes in old furniture are no longer active. Before you treat anything, find out whether the infestation is still alive. Treatment takes time and money, and sometimes you only need to repair damage that’s already there. For the wider restoration sequence, see the antique furniture restoration guide.
Is the infestation still active?
Look at the holes and the powder around them:
- Fresh holes have clean, pale, sharp edges. You may also see fine, cream-colored powder called frass, which larvae push out.
- Old holes are darker, and often filled with dirt or old wax.
To check, seal a few holes with wax or tissue, then look again after the next emergence season. If new holes appear, the infestation is probably still active. Falling dust alone isn’t proof, since moving a piece can shake out old frass.
Holes don’t always mean a live infestation. They don’t prove age either, because reproductions can be drilled and reused wood can carry old holes.
Identify the beetle from the holes
Exit hole size and location give clues to the beetle:
- Common furniture beetle (Anobium punctatum), the usual culprit in the UK and Europe, leaves round holes roughly 1 to 2 mm across. It favors sapwood, softwood, and plywood.
- Lyctus powderpost beetles leave holes around 1 mm across. They attack the starchy sapwood of hardwoods such as oak, ash, and walnut.
- Deathwatch beetle holes are around 3 mm.
- House longhorn beetle holes are oval and much larger, roughly 6 to 10 mm.
Hole size is a clue, not proof. A pest specialist or conservator can identify the species if it matters for the treatment.
Treat only an active infestation
If the infestation is active, treat it. Common options include:
- Insecticide fluid labeled for woodworm, injected into the exit holes. Most fluids work best on bare wood and don’t penetrate finished surfaces well, so check the label.
- Borate treatments, which are generally for bare wood only.
- Freezing a sealed piece or small item at about −18°C (0°F) or colder for several weeks, then thawing it slowly while still bagged. Protocols vary, and most furniture won’t fit in a freezer.
- Heat or oxygen-free (anoxic) treatments, which are professional or museum methods. Heat can damage glue and finishes.
Damp wood invites infestation. Wood moisture above roughly 12 to 16 percent makes it more likely, so keep the piece dry and stable.
Wax fillers don’t kill larvae
Filling holes with wax may hide them and keep out dust, but it doesn’t kill larvae. Colored wax sticks are useful for cosmetic repairs once the wood has been treated. Leaving old holes unfilled is also acceptable.
Is WD-40 a woodworm treatment?
No. WD-40 is a general-purpose lubricant. It isn’t labeled or tested for killing wood-boring insects, and it can leave an oily film that gets in the way of later finishing. The same problem comes up when people use WD-40 on scratches. Use a product labeled for woodworm, and follow its directions.
Strengthen weakened wood
Heavily tunneled wood can crumble. Consolidate it with a reversible product, such as Paraloid B-72 dissolved in acetone, and test on a hidden area first. Low-viscosity epoxy can also be used, but it’s very hard to reverse, so treat it as a last resort and check with a conservator.
Badly weakened legs or rails may need splicing or replacing, as described in how to repair antique furniture legs. Keep any original parts you can, and note where new wood has been added.
Keep it dry and stable
Keep the piece in a stable room, away from damp basements and hot attics, and check for new holes each season. The humidity and storage advice in what not to do to antique furniture also helps keep wood dry enough to discourage infestation.
Safety with insecticides
- Permethrin, an ingredient in some woodworm fluids, is highly toxic to cats and harmful to aquatic life. Keep pets away while you work, and dispose of leftover product as the label directs.
- Wear gloves and eye protection when injecting fluid.
- Ventilate the room, and follow the label on how long to keep it clear.
When to call a professional
Call a conservator or pest specialist if:
- the legs, joints, or other structural parts are badly damaged
- the infestation is large or spreading
- the piece is valuable enough that a wrong treatment would cost a lot
- heat or oxygen-free treatment seems necessary