Woodworm is the common name for larvae of the common furniture beetle that bore into and feed on wood, leaving behind small round holes and fine dust. Despite the name, these aren’t worms at all. They’re the grub stage of a small beetle that lays its eggs in cracks and crevices of timber, and the larvae can spend years quietly eating through your furniture before you ever notice a problem.
What Causes Woodworm
The culprit in most cases is the common furniture beetle. Adults are small, between 2.5 and 5 mm long, dull reddish to dark brown, with fine grooves running along their wing cases. Their head is almost entirely hidden beneath a strongly humped midsection that looks a bit like a monk’s cowl. You’re unlikely to spot the adults since they only live about 20 to 30 days after emerging, typically from late spring to early autumn.
The real damage happens underground, so to speak. Female beetles lay eggs in small cracks or old exit holes in the wood. Once hatched, the cream-colored, C-shaped larvae tunnel through the timber for anywhere from two to five years, feeding on the wood as they grow. When they finally mature into adult beetles, they chew their way out, leaving the characteristic round exit holes that are 1.5 to 2 mm wide.
How to Spot Woodworm Damage
The most obvious sign is small round holes scattered across the wood surface, each roughly the diameter of a pin head. But exit holes alone don’t tell you whether the infestation is still active or whether the beetles left years ago. Old, inactive damage is extremely common in antique furniture and doesn’t necessarily mean your piece needs treatment.
The key indicator of active woodworm is frass: a fine, light-colored dust that collects near the holes or falls onto surfaces below. Frass looks like very fine wood shavings and has a distinctly gritty texture when rubbed between your fingers, which distinguishes it from ordinary sawdust. If you see small piles of this gritty dust near exit holes, especially during spring and summer, larvae are likely still feeding inside.
A simple test: place the piece of furniture on a white cloth or sheet of paper and leave it for several days. Tap the wood firmly around the holes. If no dust appears on the cloth and nothing falls out when you tap, the infestation is almost certainly old and inactive. Fresh exit holes also look clean-cut and light-colored inside, while old ones darken over time and may have rounded edges.
Does Dry Wood Protect Against Woodworm?
There’s a widespread belief that keeping wood dry will prevent or stop woodworm, and while moisture does play a role, the reality is more complicated. Higher moisture levels (above 20%) create ideal conditions for larvae, which is why woodworm is more common in damp basements, garages, and poorly ventilated rooms. But larvae can survive and continue feeding in timber with moisture content as low as 9% to 12%, levels commonly found in well-ventilated, centrally heated homes.
So while reducing humidity and improving ventilation can make your furniture less attractive to egg-laying beetles, drying alone won’t reliably kill larvae already inside the wood. If you have confirmed active woodworm, you’ll need a more direct approach.
Chemical Treatment Options
The most common active ingredient in woodworm killers is permethrin, an insecticide that penetrates the wood and kills larvae as they feed. It’s available as a brush-on liquid or spray from most hardware stores.
For furniture with a paint or varnish finish, the thorough approach is to strip the surface completely by sanding or using a chemical stripper before applying the treatment. The liquid needs to soak into the bare wood to reach the larvae inside their tunnels. Some people choose to treat only the visibly affected area and then recoat, though this is less reliable since larvae may be tunneling in sections that look fine on the surface.
After applying the treatment, allow six to eight hours of drying time per coat. Wait a full 48 hours before applying any topcoat like paint, oil, or varnish. Keep the room well ventilated during application and while the product dries. Wear gloves and a mask throughout. Permethrin at these concentrations is not considered dangerous to humans, and treated surfaces are safe for children and pets once fully dry, particularly if you apply a topcoat over the treated wood.
Heat and Freezing Treatments
If you’d rather avoid chemicals, temperature extremes can kill woodworm at every life stage, including eggs. These methods work well for smaller furniture pieces and objects that can fit in a freezer or oven.
For freezing, seal the item in a plastic bag and place it in a freezer set to at least minus 4°F (minus 20°C) for seven days. This is generally effective against all life stages. Most home chest freezers reach this temperature, but a kitchen freezer/fridge combination may not get cold enough, so check the settings first.
Heat treatment works faster. Set your oven to its lowest temperature, which typically produces around 150 to 170°F. Place the item inside for 45 minutes to one hour. Thicker wooden objects (several inches or more) may need additional time. After heating, turn off the oven and let the item cool down inside for another hour before handling it. Obviously, this only works for items small enough to fit in your oven, and you should remove any hardware, fabric, or glued joints that might be damaged by heat.
For larger furniture pieces that won’t fit in a freezer or oven, professional heat treatment services can raise the temperature of an entire room or chamber to lethal levels. This is more expensive but avoids chemicals entirely.
Preventing Reinfestation
Once you’ve treated a piece of furniture, the goal is to make it unappealing to any future beetles looking for a place to lay eggs. A sealed surface is your best defense. Beetles need access to bare wood, specifically small cracks, rough grain, or old exit holes, to deposit eggs. Finishing your furniture with varnish, wax, oil, or paint closes off those entry points.
Pay special attention to the undersides, backs, and interiors of furniture, since these unfinished areas are where beetles most commonly lay eggs. If you’re buying secondhand or antique furniture, inspect these hidden surfaces before bringing the piece into your home. Look for exit holes, and if you find them, run the frass test before deciding whether treatment is needed.
Keeping indoor humidity moderate also helps. Good ventilation, avoiding storing furniture in damp outbuildings, and keeping rooms reasonably warm all make the wood less hospitable. None of these steps guarantee prevention on their own, but combined with a properly sealed finish, they make reinfestation unlikely.