Antique Wood Woodworm: How to Choose the Right Treatment (and Not Destroy the Piece)

🔍 The moment you notice the holes — and don’t know if it’s too late

You move an antique piece of furniture and find a small pile of dust on the floor. You look up and see a handful of tiny round holes on the surface of the wood. In that moment the first question is not “what do I do?” — it’s “are they still working in there?”. Answering this question is step zero, because treating a concluded infestation with an aggressive method is pointless and often harmful, whereas ignoring an active one can mean losing structural integrity within just a few seasons.

The common furniture woodworm, Anobium punctatum, measures between 2.5 and 5 mm as an adult, has a colour ranging from dull reddish-brown to dark brown, and leaves round exit holes of 1.5–2 mm accompanied by coarse-grained frass — under a microscope, the shape is recognisable as a barley grain. Lyctus brunneus, on the other hand, produces an extremely fine powder almost like flour, with galleries running parallel to the grain. It attacks the sapwood of large-pored hardwoods — oak, chestnut, ash, elm — but only if the starch content exceeds 3%, and since starch decreases with ageing, a Lyctus infestation becomes unlikely after 10–15 years. To determine whether the infestation is still active, the Canadian Conservation Institute recommends taping a piece of polyethylene film over the suspected holes with adhesive tape and removing it within two weeks: if frass continues to accumulate beneath the holes of an untouched object, the battle is still ongoing.

📊 Comparison of the three main treatments: cold, anoxia and heat

Before choosing, you need to know what you are dealing with. Each method has a precise window of applicability and equally precise risks.

For a comprehensive overview, you can find the dedicated guide here.

⚙️ How to apply each method: practical technical guidelines

What works — Freezing at −20 °C:

• Seal the object in a transparent polyethylene bag, preferably heat-sealed, with a minimum thickness of 150 microns (6 mil).
• Keep the piece at −20 °C for a full week without interruption.
• After treatment, leave the object still bagged for at least a full day before opening the bag: condensation will form on the outside of the bag, not on the wood.
• Keep the object in quarantine for three weeks or more after treatment, to intercept any surviving eggs or pupae that are not visible.

What does not work — Freezing:

• Opening the bag immediately after removing it from the freezer: condensation deposits directly onto the wood.
• Using this method on objects with oil paint, linseed oil films or synthetic polymers without a prior assessment: between −20 °C and −30 °C there is a concrete possibility of increased craquelure.

What works — Anoxia:

• Use heat-sealable barrier films and oxygen absorbers — the NPS Conserve O Gram 3/9 technical reference cites Ageless Z absorbers by Mitsubishi Gas Chemical Company.
• Monitor with the Ageless Eye indicator: it changes from purple to pink when oxygen drops below 0.5%, the threshold required for effectiveness.
• Maintain the treatment for at least two weeks at room temperature.

What does not work — Anoxia:

• Exceeding 1% residual oxygen: above this threshold the treatment is not effective.
• Expecting anoxia to also eliminate fungi: it does not.

What works — Heat treatment:

• Do not exceed 55 °C: at this temperature insect mortality is almost instantaneous according to the Canadian Conservation Institute.
• Calculate timing based on the rate of heat penetration into the material, which is the true limiting factor.

What does not work — Heat treatment:

• Raising the temperature to shorten the time: exceeding the threshold damages adhesives, inlays and historic finishes.
• Applying it without monitoring the internal temperature of the wood with a dedicated sensor.

✅ The most common mistakes and the checklist before taking action

Typical mistakes that make the situation worse:

• Taking action without verifying whether the infestation is still active. Treating a concluded attack with invasive methods damages the piece without any benefit.
• Not quarantining the object before and after treatment. The Canadian Conservation Institute recommends sealing objects of uncertain status in heavy polyethylene for one to two months, checking them periodically.
• Using freezing on furniture with mixed components without evaluating each material individually.
• Relying on surface chemical products for deep infestations: surface treatments do not reach the internal galleries where the larvae live.
• Ignoring humidity as the primary cause. Anobium punctatum larvae cannot establish themselves below 65% relative humidity, which corresponds to a wood moisture content of 15%. If you do not control the environment, any treatment is only temporary.

When to consult a professional: if the object contains heterogeneous materials (metals, fabrics, gilding, paintings), if you cannot identify the type of insect, or if structural damage is already advanced, DIY intervention risks causing more damage than the woodworm itself.

Operational checklist before any treatment:

• ☐ Have you verified that the infestation is active using the adhesive tape over the hole method?
• ☐ Have you identified the species (Anobium or Lyctus) based on the type of frass and the wood affected?
• ☐ Have you measured the moisture content of the wood?
• ☐ Have you assessed all the materials present in the object before choosing a method?
• ☐ Have you set up an isolated quarantine area?
• ☐ Have you planned post-treatment monitoring for at least three weeks?

📖 Find the complete guide here

❓ FAQ — Frequently asked questions

How can you tell if a woodworm infestation in antique wood is still active?
Fix a piece of transparent polyethylene with adhesive tape over the suspected holes and remove it within two weeks. If new frass has accumulated beneath the hole on an untouched object, the infestation is active. Exit holes with sharp, clean edges also indicate recent activity, whereas dark, worn edges suggest a past attack.

What is the correct temperature for anti-woodworm freezing and for how long?
The standard treatment indicated by the Canadian Conservation Institute requires −20 °C for one week, with the object sealed in preferably heat-sealed transparent polyethylene. After treatment, the object must remain bagged for at least one day at room temperature, so that condensation forms on the outside of the bag and not in contact with the wood.

Is anoxic treatment safe for all types of antique wood?
Anoxia is one of the least invasive methods available, but it does not kill fungi: if the infestation is accompanied by a fungal attack, an additional intervention will be required. To be effective, the oxygen level must drop below 0.5% — above 1% the treatment does not work. NPS Conserve O Gram 3/9 recommends oxygen absorbers such as Ageless Z and the Ageless Eye indicator to monitor the threshold.

Does Lyctus brunneus also attack antique wood that is many decades old?
No, generally speaking. Lyctus brunneus requires a starch content greater than 3% in the sapwood of large-pored hardwoods. Since starch decreases as wood ages, a Lyctus infestation becomes unlikely after 10–15 years from the time of processing. On very old wood, Anobium punctatum is far more likely to be the culprit.

Which materials cannot withstand freezing at −20 °C and need to be carefully assessed?
CCI Note 3/3 warns that rubber, linseed oil films (oil paint) and synthetic polymers become brittle between room temperature and −30 °C. On painted or varnished objects there is also a real, though limited, possibility of increased craquelure between −20 °C and −40 °C. Before freezing a piece containing these components, a case-by-case material assessment is essential.

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