Renovating

Combating woodworm: how to fully eradicate the problem

Arne Schätzle

Whether they attack an antique cabinet or a load-bearing roof truss: woodworms like to eat through all types of wood. Read here how to recognize an infestation and how to effectively combat this pest.

A man kneels in an unclad attic with a double meter in his hand. A window is visible in the background.
© Getty Images/Cultura RF

In this article

What is a woodworm?

The term “woodworm” usually refers to the larvae of the common furniture beetle, also known as the common house borer (Anobium punctatum), or of the house longhorn beetle, also called the old house borer or European house borer (Hylotrupes bajulus). While adult common furniture beetles don’t cause much damage, their larvae tirelessly eat their way through pieces of furniture or load-bearing wooden structures, because wood is the insects’ only food.

The common furniture beetle and the house longhorn beetle are widespread throughout Europe. The female woodworm lays eggs in wood crevices. Once the larvae have hatched, they start eating the wood and continue to do so until pupation. This can take three to eight years, by which time the pests may have completely destroyed the wood.

Where does the woodworm nest?

The house longhorn beetle is found primarily in the roof area because the beams are mainly made of coniferous wood, which is what woodworms prefer – i.e. pine, spruce and fir. The roof trusses of new buildings made of young fresh wood are particularly at risk. Old wood, on the other hand, is less attractive to the house longhorn. Unfortunately, simply avoiding conifers is no guarantee – the common furniture beetle also eats hardwoods.

It can’t survive in hard heartwood, but only in soft sapwood – this term designates the young wood under the bark, which is particularly rich in protein. This favors the development of woodworm because the pest itself consists largely of protein.

House longhorn larvae require a minimum wood moisture content of more than 12 percent. Ideally, they even prefer around 30 percent. This is another reason why they don’t tend to nest in the wooden components of centrally heated rooms, but rather in construction wood outdoors, in wooden paneling or furniture in basements, in wooden floors, or in stairs and barns.

How do I recognize a woodworm infestation?

You can recognize a woodworm infestation by the holes measuring one to two millimeters that appear in the affected wood. Since these holes are difficult to make out by sight, testing with wood flour is recommended. Even then, you won’t be able to see much with the naked eye, but there is a trick to make the wood flour visible: place dark paper under a suspicious spot. If wood dust collects on it, a woodworm has probably taken up residence inside. The greater the amount of bore dust, the more advanced the infestation by the insects. Unfortunately, if the roof truss is clad, there is no choice but to remove the cladding to inspect the roof truss.

Tip: be patient because young larvae sometimes stop feeding for a few days. You may well have to wait a little longer to be certain.

A piece of wood is heavily infested with woodworm.

You can tell if a piece of furniture or parts of the house are infested with woodworm by the holes measuring one to two millimeters that appear in the affected wood.

How can I combat woodworm?

There are numerous methods and means of getting rid of woodworm. They range from home remedies to calling in an exterminator. The method that is right for you depends partly on the object being attacked, i.e. furniture or actual components of the house, as well as on the severity of the infestation. In any case, the sooner you detect and combat a woodworm infestation, the greater the chances of getting rid of the wood pests again quickly.

1. Prevention: avoiding woodworm

Of course, it’s best if woodworm doesn’t spread in the house and furniture in the first place. It’s important to note that the more moisture there is in the wood, the greater the risk of a woodworm infestation. You should therefore make sure that construction wood is properly dried and isn’t left lying on the ground outside.

Instead, place posts or beams under the wood so that it is not in direct contact with the ground. Otherwise it will be difficult to dry it out completely due to damp from the ground. Store wood in a sunny location with a good supply of air. It should preferably be placed under a roof, so that it is protected from the rain as well.

As a preventive measure, treat construction wood outdoors with weather-protective glazes that have a water-repellent effect and protect against the light. In addition, you should examine this type of wood – as well as your roof truss – on a regular basis. Check for moisture and make sure there are no woodworm infestations.

A normal wood glaze doesn’t contain biocides that kill woodworm, but still acts as prevention because it has one important property: it keeps moisture away – and hence also woodworm. A glaze prevents water from penetrating the wood, creating a climate that is permanently unfriendly to woodworm. Other low-pollutant agents may include waxes, paints or varnishes. Applying cedar oil can help. This protects against pesky woodworms and also gives an elegant shine to your furniture.

2. Combating woodworm with extreme temperatures

Strong heat is just as bad for woodworm as extreme cold. The larvae of the insects die at above 55 degrees Celsius, which is a temperature that your oven reaches with ease. If you have small items of infested furniture, you can place them in the oven to drive out the woodworm.

If, on the other hand, woodworm has attacked an antique chest of drawers, chest or cabinet, you can carry out the heat treatment in a sauna. In the summer, you also have the option of simply placing your furniture in the sun and wrapping it in black film to enhance the effect of the heat.

Cold is also a proven remedy against woodworm. You can treat small furniture in a freezer or place larger wooden furniture outside in winter temperatures of at least minus ten degrees – provided that you have a dry shelter.

3. Combating woodworm with home remedies

If the infestation is not yet too far advanced, home remedies can also help to drive away the pests: use a syringe to introduce vinegar essence into the holes. This is not only a great immediate help against woodworm, but also offers good protection in the long term. Alternatively, you can insert boric salt mixed with water into the holes. Boric salt is non-toxic and – unlike vinegar – odorless.

You can also spray the affected wood with the salt solution from the outside. Repeat the process twice within 24 hours. However, this procedure doesn’t usually reach the worms that have already worked their way deeper into the wood. Another idea that may help is to seal the holes with beeswax. This gradually causes the woodworms to suffocate. However, this can be a very tedious and lengthy job.

When treating solid wood or large, heavy furniture, you can use acorns as bait: the smell attracts the wood pests so that they will bore holes in the acorns. Place some of the nuts near the infested area. Repeat this process several times. This measure is somewhat lengthy, but usually achieves the desired effect. You can tell the method is working if there are small holes in the acorns. Then you can simply dispose of them along with the worms.

An acorn can be seen lying on a wooden surface.

Bait the worms with acorns: the smell of acorns attracts woodworms, so they will abandon the wood and bore into the acorns instead.

4. Isopropanol, ammonia and woodworm killer

Cleaning alcohol, or isopropanol, is one of the most effective non-toxic home remedies, as the substance is deadly to woodworms. Isopropanol can be obtained relatively cheaply from pharmacies. However, the agent may attack paint, glaze or varnish. You should therefore test beforehand whether your piece of furniture – and the paint on it – will withstand the alcohol.

You should only use isopropanol in a very well-ventilated area because of the risk of explosion. Work outdoors if possible. Apply the undiluted alcohol directly to the furniture with a brush. To stop evaporation, wrap it in film. It takes about three days for the alcohol to take effect. However, it won’t reach the deepest areas if the wood is more than five centimeters thick.

Treatment with ammonia solution works in the same way. You can also inject the ammonia water into the boreholes with a syringe. A liter can be purchased for about four or five francs. In addition, specialized stores sell ready-made woodworm killer that can be applied to the wood with a syringe, brush or spray bottle.

The most important questions and answers at a glance

What is a woodworm?

The term “woodworm” usually refers to the larvae of the common furniture beetle, also known as the common house borer (Anobium punctatum), or of the house longhorn beetle.

Where does the woodworm nest?

Woodworm and house longhorn beetles prefer to nest in construction wood, for example in furniture or in the attic.

What type of climate do woodworm and house longhorn beetles prefer?

Both furniture beetles like damp wood and indoor air that isn’t too dry.

How do I recognize a woodworm infestation?

You can recognize a woodworm infestation by the holes measuring one to two millimeters that appear in the affected wood.

How can I get rid of woodworm?

There are a number of home remedies that you can use to get rid of woodworm. These include glazes, oils, salts and acids, as well as extreme temperatures.

Conclusion: stay alert

There are several different factors that determine the most effective method of combating woodworm. The most important criteria are the type of object or area that is infested and how far the infestation has already progressed. Many methods are quite straightforward but take time. If any important components of the house, such as the attic or the framework, are severely affected, only a professional can help – which is when things can get expensive. That’s why it’s particularly important to always keep a close eye on vulnerable areas and objects.

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