Is it really woodworm?
In Ireland, "woodworm" almost always means the common furniture beetle, Anobium punctatum. The worm is the larva. It lives inside the wood for a few years, eating tunnels, then turns into a small brown beetle and chews its way out. What you see are the exit holes it leaves behind: round, clean holes about 1 to 2 mm across, and a gritty, pale dust called frass. Rub a pinch of it between your fingers and you can feel tiny pellets, a bit like fine sand.
The beetle prefers unfinished softwood and sapwood, so on a piano it rarely goes for the polished outside. Look inside and underneath instead:
- •the back frame and the heavy back posts of an upright
- •the underside and back of the keybed, the shelf the keyboard sits on
- •the bottom board, behind the lower front panel
- •plywood panels and any bare wood on the inner surfaces of the case
A torch and five minutes with the lower panel off will tell you more than the outside of the piano ever will.
Active, or old and finished?
This is the question that matters most. A lot of older pianos in Irish homes have a few holes from an infestation that died out decades ago. That is history, not a problem. Signs that the beetle is still at work:
- •Fresh, pale dust below the holes, on ledges inside the case, or on the floor under the piano.
- •Sharp, clean edged holes with light coloured wood inside. Old holes are dark, dusty and worn round at the edges.
- •Dead beetles in the bottom of the case, or on the nearest windowsill, where they head for the light.
- •The time of year. Adults come out roughly between May and September, so new holes and dust show up in summer.
A simple test
Vacuum the area clean, then stick tissue paper or a strip of masking tape over the holes. Leave it through the summer. If anything has chewed through, or fresh dust has appeared, it is active. If the paper is untouched and nothing new has fallen by autumn, you are most likely looking at an old, dead infestation.
What gets mistaken for woodworm
When someone rings me about woodworm, it often turns out to be something else. These are the usual suspects:
| What it is | How to tell |
|---|---|
| Clothes moth larvae | The most common pest I find in pianos. Damage is in the felts and cloth: hammers, dampers, key bushings, the cloth under the keys. Look for bald patches, silky cocoons and fine debris under the action. |
| Carpet beetle larvae | Small, hairy, slow moving larvae and their shed skins. They also eat felt and wool, so the damage looks much like moth. |
| Mice | Droppings, nests of shredded felt or paper, chewed key covers and a stale smell. Urine also corrodes strings and tuning pins. |
| Old tack, pin and screw holes | Left by earlier repairs. Often square, or in neat rows, and never with dust coming out. |
| Open grain in oak or ash | Natural pores in the wood surface. They are shallow and do not lead into tunnels. |
| Old treatment holes | A neat drilled grid, sometimes filled with wax. Someone has already treated the piano at some point. |
| Damp and rot | Wood that is soft, dark and musty, often with mould on the felts. Damp is frequently the reason beetles got going in the first place. |
A few rarer beetles are worth knowing about. The powderpost beetle leaves very fine, floury dust and goes for unfinished hardwoods. The house longhorn makes much bigger oval holes, 6 to 10 mm, and is rare in Ireland. The deathwatch beetle makes holes about 3 mm across and lives in structural oak, so if you find it, look at the floorboards and skirting as well. The house may be the source, not the piano.
Where the damage is decides whether it is worth fixing
Ten holes in the wrong place matter more than a hundred in the right one. This is roughly how I weigh it up:
The pinblock (wrest plank)
The worst place. The tuning pins rely on tight wood to hold the strings at tension. If the block is tunnelled, the pins go loose and the piano will not hold a tune. On most pianos that is the end of the road. I explain more about loose pins in why a piano will not stay in tune.
Back posts, frame and keybed
These carry the load. I probe them with a fine tool: sound wood resists, tunnelled wood crumbles. Light damage can be lived with once it is dead. Heavy damage here weakens the structure.
Action and keys
Damaged action parts and keys can be replaced individually, so this is usually a repair job rather than a verdict on the piano.
Case and panels
Mostly cosmetic. Once any activity has stopped, the holes can be filled and the piano played for years.
Treating it properly
Only treat if the woodworm is active, or if you genuinely cannot tell. There is no point soaking a piano in insecticide for holes that are sixty years old. When it does need doing, this is the order I follow:
- Take the action and keyboard out, then vacuum the whole inside of the case thoroughly, including the bottom board and every ledge.
- Apply a permethrin based woodworm treatment, the kind sold in Irish hardware shops, and follow the label. It goes on bare, unfinished wood only.
- Inject it into the flight holes. Brushed on, the fluid only gets a few millimetres into the wood, and the larvae are deeper than that.
- Keep it well away from felts, cloth, leather, hammers, strings and the face of the soundboard. Test it on a hidden spot first, because it can mark a polished finish.
- Deal with the removed wooden parts separately, or replace them. Small loose wooden parts can be frozen instead: sealed in a bag, at about minus 20°C or colder, for at least two weeks. Never freeze veneered or inlaid parts, and never use heat. Glue joints, felts and finishes all suffer.
If the real culprit is moth, insecticide on the wood does nothing. The eaten felts need cleaning or replacing, and a moth deterrent inside the case helps keep them away.
For a valuable or historic instrument, there is the method museums use: an oxygen free (anoxic) treatment, where the piano or its parts are sealed in an enclosure with the oxygen removed for several weeks. No chemicals, and it kills every stage from egg to beetle. It is specialist work and it is not cheap, so it only makes sense on a piano worth the money.
Afterwards
- •Fill visible holes with coloured wax, so any new ones stand out next summer.
- •Keep the piano off damp outside walls. Damp wood is what the larvae like.
- •Check it again the following summer for fresh dust.
- •Check the other furniture and the floorboards in the room. It spreads.
Safety
Woodworm treatments are pesticides. Wear gloves and a mask, keep the room well ventilated, follow the label to the letter, and keep children and pets away until everything is dry.
When it is not worth it
I would rather tell you this straight than sell you a repair that will not last. If the woodworm is active and it is in the pinblock or the structural parts, the cost of stripping, treating and rebuilding is more than most ordinary uprights are worth. In that case the honest advice is usually to get the piano out of the house, before the beetles move on to your floorboards and furniture.
The same goes when you are buying. If a second hand piano has fresh dust under it, walk away or price it accordingly. There is more on what to look for in my guide to buying a second hand piano in Ireland.
Questions people ask me
Can woodworm spread from a piano to my furniture?
Yes, if the infestation is active. The adult beetles fly in summer and lay eggs on bare, unfinished wood, so floorboards, the backs of wardrobes and old furniture in the same room are all at risk. An old, dead infestation with no fresh dust cannot spread.
Is a piano with woodworm worth saving?
It depends on where the damage is, not just whether there are holes. Old holes in the case or back panels are usually cosmetic. Active woodworm in the pinblock, back posts or keybed is serious, and on most ordinary uprights it means the piano is not worth the cost of treatment and repair.
Can I treat woodworm in a piano myself?
You can treat bare, unfinished wood on the outside of the case yourself with a permethrin based woodworm treatment, following the label. Inside the piano it is different: the action and keyboard have to come out first, and the fluid must be kept off the felts, hammers, strings and soundboard. That part is best left to a technician.
Is it woodworm or moths?
Look at what is damaged. Woodworm leaves round holes in wood with gritty pale dust. Moths eat felt and cloth, so you see bald or eaten hammers, dampers and key felts, with silky cocoons and fine debris under the action. In pianos, moth is far more common than woodworm.