Woodworm leaves a handful of telltale signs in furniture, and the most obvious is small round exit holes in the wood’s surface, typically 1 to 3mm in diameter. But holes alone don’t tell the full story. Knowing what to look for, and whether the infestation is still active, determines whether you need to act urgently or simply keep an eye on things.
Exit Holes: Size and Shape Matter
The round holes you see on the surface of furniture are where adult beetles chewed their way out after maturing inside the wood. The size of these holes tells you which type of beetle you’re dealing with. The common furniture beetle, the species responsible for most household woodworm, leaves holes between 1.6 and 3mm across, roughly the diameter of a pin head. Powderpost beetles, which target hardwoods like oak and ash, leave much smaller holes: 0.8 to 1.6mm. If you spot larger holes in the range of 3mm, you may be looking at deathwatch beetle damage, which tends to affect older, often damp hardwood furniture and structural timbers.
The holes are almost always circular. If you see oval or irregularly shaped holes, that’s more likely mechanical damage or a different type of insect entirely.
Frass: The Sawdust That Gives It Away
Frass is the fine dust that wood-boring larvae produce as they tunnel through timber. It’s one of the most reliable signs of woodworm, and its appearance varies depending on the species. The common furniture beetle produces light-colored frass that looks like very fine wood shavings. You’ll often find it sitting in small piles beneath exit holes, on shelves, or on the floor under affected furniture.
Powderpost beetle frass has a distinctly different texture. It feels and looks like flour or talcum powder, much finer than what the furniture beetle leaves behind. This ultra-fine dust often falls out of exit holes and accumulates on surfaces below the infested piece. Deathwatch beetle frass is different again: small, rounded pellets that resemble tiny buns, often found clustered around the holes.
The type of frass you find helps with identification, but its freshness is what really matters for determining whether the problem is current.
Active vs. Inactive Infestations
Many pieces of old furniture have woodworm holes that are decades old. The beetles are long gone, the damage is done, and no treatment is needed. Telling the difference between an active and inactive infestation comes down to a few details.
Active exit holes look clean and fresh. The edges are sharp, and the interior of the hole appears light-colored, matching the tone of freshly exposed wood. Inactive holes, by contrast, look darker, worn, and may have rounded or softened edges. They often accumulate dust, dirt, or old polish inside them.
Fresh frass is the strongest indicator of current activity. If you see light-colored, powdery dust around or beneath holes, that’s a sign larvae are still tunneling or adult beetles have recently emerged. Old frass tends to darken over time, clump together, or disappear entirely.
You might also notice damaged or crumbling wood around the affected area. If the surface yields slightly when you press it, or the wood sounds hollow when you tap it with a knuckle, the internal tunneling may be extensive. Cracks or crumbling patches on the surface point to significant structural damage beneath.
A Simple Test for Active Woodworm
If you’re unsure whether your furniture has an active infestation, there’s a straightforward test you can do at home. Locate the exit holes, then cover them with strips of masking tape. Press the tape down firmly, using the handle of a paintbrush or a similar tool to make it as flush with the surface as possible. Don’t use paint or varnish to seal the holes, since you’ll need to remove the covering later if treatment is needed.
Then wait. Wood-boring beetles typically emerge in spring and early summer, so apply the tape before that season begins. If by May or early June the tape remains intact with no new holes punched through it, the infestation is inactive. If you see one or more small punctures where beetles broke through the tape, you have an active problem that needs attention.
For powderpost beetles specifically, Oklahoma State University Extension recommends a quicker check: dust off the wood surface around suspected holes and wait 24 hours. If fresh, flour-like dust reappears around the holes, the beetles are still active.
Other Signs You Might Spot
Beyond holes and frass, keep an eye out for the beetles themselves. Adult furniture beetles are small, brown, and roughly 3 to 5mm long. You might find them near windows or light sources after they emerge, since they’re attracted to light. Dead beetles on windowsills near affected furniture are a useful clue, especially during spring and summer.
In some cases, you’ll notice the wood itself weakening before you spot any holes. Legs of chairs that suddenly feel wobbly, shelves that bow unexpectedly, or edges that crumble when handled can all point to internal tunneling that hasn’t yet produced visible exit holes. The larvae spend years feeding inside the wood before emerging as adults, so structural weakening sometimes shows up first.
Which Furniture Is Most at Risk
Woodworm larvae prefer wood with some moisture content. Furniture stored in damp environments like basements, garages, sheds, or unheated rooms is far more vulnerable than pieces kept in dry, centrally heated living spaces. Antique furniture and secondhand pieces deserve a careful inspection before you bring them into your home, since they can introduce an infestation to other wooden items.
The common furniture beetle attacks both softwoods and hardwoods, making most wooden furniture a potential target. Powderpost beetles are more selective, preferring hardwoods with large pores and high starch content, such as oak, ash, and walnut. Plywood, chipboard, and veneered furniture are generally less susceptible, though not immune if they contain real wood layers.
What to Do if You Confirm an Infestation
For smaller furniture items with confirmed active woodworm, freezing is an effective and chemical-free option. The piece needs to reach at least minus 18°C and stay at that temperature for a minimum of 48 hours. This kills all life stages, including eggs, larvae, and adults. Some specialist services use industrial freezers large enough to handle full-sized furniture, typically holding items for about 72 hours at minus 20°C to ensure complete elimination.
Chemical treatments are also widely available as brush-on or spray products that penetrate the wood and kill larvae in their tunnels. For larger or more valuable pieces, professional treatment may be worthwhile, particularly if the structural integrity of the furniture is already compromised. A professional can assess the depth of damage and determine whether the piece is still sound enough to use or needs repair alongside treatment.