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The house longhorn beetle

The house Do you sometimes hear suspicious noises in the woodwork in your home (beams, furniture, etc.)? It could be longhorn beetle larvae having a meal ! In this dossier, you'll find a range of answers and natural products to help you combat this wood-eating insect. 

I would like to

Find out more about longhorn beetle

(identity, feeding habits, reproduction, etc.)


Combat the longhorn beetle

(method of action, natural insecticides, etc.)


Who is the house longhorned beetle ?

HYLOTRUPES BAJULUS - House longhorn beetleLatin name : Hylotrupes bajulus
Order : Coleoptera
Family : Cerambycidae
Adult size : 10 to 20 mm
Size of the larva : 20 to 25 mm
Location : in woodland
Period : all year round

This insect is very common in nature. It feeds exclusively on wood, and more specifically on softwood. Its favourite species include maritime pine, laricio pine, Austrian black pine and Scots pine, as well as larch, spruce and fir...., to name but a few ! 

It does very well on debarked wood, and just as well on "worked" wood, which is why it is so keen on carpentry, and occasionally on smaller items such as the door frames in your home.

As the adult insect has a very short lifespan (around 1 month) and does not feed during this period (reproduction), it is the larva which, as it develops over the years, will do the most damage. It looks like a large white worm measuring 20 to 25 mm in length, with an enlarged, flattened front.  

What you need to know about the house longhorn beetle

HYLOTRUPES BAJULUS - House longhorn beetle

The house longhorned beetle mainly attacks well-dried, dead softwood or construction wood such as larch or spruce, but also oak sapwood.

The larva bores a network of galleries, the walls of which are finely sculpted by its mandibles.

As long as the larvae are able to feed, the beetle will remain in the wood.

Apart from the characteristic sound of the larvae gnawing away at the wood, it is difficult to detect its presence. Holes can be an excellent clue to its presence, but there are never many of them, and they are not always visible (behind your insulation, for example). Finding the insect, dead or alive, is also possible, but no less uncertain, especially as the insect is small. Finally, if you find sawdust, take a close look, as it is not uncommon for its compaction in very shallow galleries to split the residual film of wood, resulting in a telltale drip. Note also that any swelling of the wood, even in a very localized area, is suspicious to say the least, and should be probed (with the tip of a knife or the blade of a small screwdriver, for example).

As it does not like cold and damp, it is more easily found in heated premises.

Capricorn beetles do not attack the heartwood, only the sapwood (which is softer).  

 Hylotrupes bajulus - capricorn housesHYLOTRUPES BAJULUS - House longhorn beetle

Development cycle : Adults emerge from the wood from mid-June to the end of August. They live for 15 to 30 days and do not feed. They devote this time exclusively to reproduction. After mating, the female lays between 40 and 100 eggs in cracks in the wood. The larval cycle lasts 3 to 5 years on average. But the length of larval development depends on the nutritional qualities of the wood, ambient humidity and, of course, temperature. The galleries dug by the larvae are oval and striated by their mandibular strokes. The adult exit holes on the surface of the wood are oval (elliptical), around 6 to 10 mm long.

Generations frequently follow one another on the same wood, especially as the capricorn beetle can occasionally reproduce without leaving its galleries, which obviously adds to its discretion and, above all, its harmfulness.


A few differences with the oak longhorn beetle

 Hesperophanes cinereus - oak capricornHesperophanes cinereus - oak longhorned beetle

There are over 25,000 species in the Cerambycidae family, commonly known as capricorn beetles. Only one species can really be considered a nuisance to our homes: the house longhorn beetle. However, it is often confused with other species in this family, in particular the oak longhorned beetle (Cerambyx cerdo or Hesperophanes cinereus ). Also known as the great capricorn beetle, the oak capricorn beetle is an insect protected by a ministerial decree dated 22 July 1993 and also at European level, via Annex II of the Bern Convention and Annex IV of the Habitats Directive. For this reason, chemical or even ecological control of the oak longhorn beetle is prohibited. It is considerably larger than the house longhorn beetle.

As its name suggests, this capricorn is mainly found in old oak trees and sometimes in old chestnut trees. It is not found in houses, unless it has wandered off. The oak longhorned beetle rarely leaves the tree from which it was born. In any case, this insect poses no danger to your home.

Development cycle : The adults emerge from the wood between May and the end of August. They live for 15 to 30 days and do not feed. The larval cycle is generally shorter than that of the house longhorn beetle (2 years or more). Damaged wood looks similar to that of the house longhorn beetle, but the galleries are larger and the exit holes more numerous.  

How can I combat the house longhorn beetle ?

HYLOTRUPES BAJULUS - House longhorn beetle

Small pieces of wood (obviously not your frame!) can be put in the freezer.

If possible, try to reduce the moisture content of the wood (drying, ventilation, heating).

According to the regulations, products used to treat wood against wood-eating insects, whether preventive or curative, must contain at least one active ingredient belonging to biocide class TP8.

The problem is that there are currently no authorised natural active ingredients in this class.

Most wood treatment products contain cypermethrin in combination with a solvent (white spirit, citrus, water, etc.). Whether they have an odour or not, these treatment products containing components of petroleum origin are not very healthy in a place where we live!

But a capricorn beetle is an insect. And to kill an insect, you use an insecticide that must be in class TP18.

You can therefore use a natural insecticide to kill capricorns. This insecticide will have no wood protection function, unlike wood treatment products. But it will get rid of the beetles.

Although it may seem obvious, don't try to treat waxed, painted or varnished wood. To be effective, the treatment must be applied to untreated wood.

The slightly time-consuming but effective solution for killing longhorned beetles is to work the insecticide into the holes made by the insects (syringe, spray, sponge, mop).


There are 3 products for this purpose :

-Our 4J All Insects insecticide (4j at 5%). This 500ml spray will treat around 5 m2. For larger surfaces, use the same product in its concentrated form and dilute to 5% yourself. Note that this product, based on plant pyrethrum, is short-lived. It will therefore be effective for rapid curative action, but not for long-term curative action. As soon as the insect comes into contact with the 4J product, it will die instantly (pyrethrum's neurotoxic effect). The difficulty remains in reaching these insects, which often take refuge in the heart of the wood. The best results are obtained by injecting the product (using a small syringe) into the largest holes left by the insect.


- Margosa Extract : Margosa's main property is to make all treated surfaces unfit for insect consumption, so the insects either have to leave the treated area in search of food, or starve to death. Thanks to its broad spectrum and long duration of action, Margosa is effective in most infested areas. It can be applied by spraying or injection. Margosa blocks the development of larvae, disrupts the search for food and sterilises adult insects. The treatment should be carried out by spraying the wood or injecting it directly into the holes at a concentration of 2% for preventive use and 4% for curative use.

Diatomaceous earth spray : If the holes (galleries) left by the insect in the wood are large enough (over 2 mm), diatomaceous earth spray in aerosol form can be used. Thanks to its applicator tube, you can apply the diatomaceous earth to each hole and inject it as deeply as possible. Thanks to the specific surface area of its grains and its siliceous skeleton, diatomaceous earth is formidable in the fight against crawling insects :

1 -  Ingestion of the silica particles (which are very sharp) by insects causes lesions in their digestive tract.

2 - The fineness and hardness of the silica particles collected by the insect's bristles cause lesions on its limbs or carapace. This causes the insect to lose body fluids, leading to death from dehydration after a few days. The absorbent properties of diatomaceous earth (up to 150% of its weight) encourage this process.


N.B.: Longhorn beetle are xylophagous insects. For all diagnoses and treatment methods concerning this family of insects, you can read our specific file on wood-eating insects. 

The products you need to combat longhorned beetles

Go directly to the detailed product sheets for products to combat longhorned beetles.

Insecticide 4J diluted 5% - All insects -...

Ready-to-use  4J insecticide diluted to 5% . With this concentration, you will destroy  most flying and crawling insects  very quickly....
In stock

4J Insecticide concentrate with plant...

4J insecticide concentrate to be diluted. Effective against a large number of crawling and flying insects in our homes. Available in...
In stock

*PAE: Ready to use


N.B.: Obviously, if the longhorn beetle invasion is serious and your wood has been under heavy attack for years, you will need to call in specialist, approved companies to carry out a full diagnosis and find appropriate solutions.


Here's what the longhorn beetle looks like in motion


Frequently asked questions about longhorned beetles

Q: We have a 7-metre section 200 x 200 mm fir beam in our living room (installed in 2007). It turns out that it is infested with capricorns on the sapwood in the horizontal part. (we hear them every day). Do you have a curative insecticide in your product range that I could apply to the surface ? It's difficult for me to get to the top of the beam (10cm from the ceiling), but I can make holes to help the product penetrate. Will a surface product be enough ?
A: You can use our 4J insecticide diluted to 5%, but to be effective, the product must come into contact with the insect either by saturating the wood or by injecting the product into the wood. Beforehand, you'll need to remove any sapwood that is damaged or no longer holding.

Q: I have to treat 145 m2 of new panelling (Douglas fir) in my house. They are infested with capricorn beetles. How do I go about it ?
A: Under the new biocide regulations, our products can no longer be used on wood-eating insects, but whatever insecticide you use, you need to treat raw wood (unpainted or varnished) with a brush until the wood is saturated, with 2 treatments 24 hours apart. Given the thinness of the wood (1cm), this should be sufficient.

Q: What product can be used to destroy longhorned beetles, and what dosage is available and preferable ?
A: Our products are not approved for treating wood.

Q: I own some old buildings in the Alpes de Haute Provence. 3 days ago and for the first time I saw insects attacking poplar beams, large piles of small shavings on the ground, the sound of flying insects and the gnawing of wood. 3 weeks before nothing, I'm very worried, this roof is 500 m² and I haven't been to see the frames that aren't visible.
A: It could be Capricorn beetles, it's the time of year when they reproduce.

Q: Can you treat just part of the wood in the house (just one room) against wood-eating insects, or do you have to treat all the wood in the house ?
A: In general, only the affected wood is treated. It is not necessary to treat healthy wood.

Q: The framework of my house is showing signs of sawdust, termites, beetles or capricorn beetles? I can't tell them apart, what product should I use, and if I need to inject it into the heart of the wood, what tool should I use ?
A: Probably house longhorn beetles, maybe furniture beetles, but in general, they're more likely to be found in furniture. Termites don't leave sawdust. Injection treatment requires equipment that you can hire (compressor, nozzle, etc.). Our 4J insecticide is apparently effective against this type of insect, although it is not approved for wood treatment.

Q: There's a tree in my garden with beetle larvae inside. I've cut it down, but there are still some in the stump. What product should I buy ?
A: Our 4J insecticide, diluted or pure, will be perfect, but this product doesn't stand up to rain. All you have to do is fill every hole in the stump to kill them and protect the whole thing with a tarpaulin while the product works. What's more, our 4J insecticide is not approved for treating wood.

Q: A friend referred me to your site because I live in an old house where the capricorn beetles are starting to cause serious damage. It seems that there are other insects making holes in the exposed beams, but they're smaller. What products can I buy from you to put an end to this problem? How is it applied? I had a company come and give me an estimate of...1,500 Euros! I find that prohibitive !
A: Before answering, I'd advise you, if you haven't already done so, to visit our special xylophagous file on our site. You should find some of your answers there. For treatment, opt for Margosa extract (an excellent repellent), which you can dilute yourself with water and a disinfectant. 1500 euros? Either these people are ill-intentioned or there's a lot of work involved. That's about 3 days' work + the products.

Q: I'm interested in treating capricorn beetles in buildings. Is the best solution the pure can ?
A: Pure insecticide is cheaper than ready-to-use, especially when it comes to postage costs (especially when you need several litres). As it's a product that can be stored and used on all insects, I think it's more interesting pure than diluted. Please note, however, that our 4J insecticide is not approved for use on wood.

Q: I've bought a house in Bergerac 24; the roof structure (50m2 of roof) has recently been reworked, but on some of the old rafters that have been preserved I suspect the presence of capricorn beetles. Would your insecticide be effective and how should I apply it? in what quantity? at what cost? what precautions should I take ?
ASince the new regulations on insecticides, apart from boron, no natural product is approved for wood treatment.
To be clear, the capricorn beetle (just like the furniture beetle, the termite or the brown wood beetle) is an insect that can be eliminated with a natural insecticide product (classified as TP18 in biocides) when you treat the insect in question in a room in the house or when it is visible and on wood. On the other hand, when you want to eliminate the insect in question in wood, and this is your case, we talk about a wood-eating insect treatment (classified as TP8 in biocides). We don't currently have any natural products classified as TP8.
As far as the use of 4J insecticide is concerned, we know that it is effective against capricorn beetles. Except that this product, based on natural pyrethrum, has a very short remanence. It is therefore effective for rapid curative action, but not for long-term curative action.
However, in your case, we can recommend Margosa extract (classified as a TP19 (repellent) in biocides).
The main property of Margosa or Neem is to make all treated surfaces unfit for insect consumption, so the insects either have to leave the treated area in search of food, or starve to death.
Thanks to its broad spectrum and long duration of action, Margosa is effective in most infested areas. Apply by spraying or injection. The organic insecticide blocks the development of larvae, disrupts the search for food and sterilises adult insects".
The treatment should be sprayed onto the wood at a concentration of 2% for preventive use and 4% for curative use.

Q: What product is used to treat longhorned beetles in structural timber ?
A: Under the new regulations, apart from boron, there are no longer any authorised natural products. You need to look at permethrin! Or with our Margosa extract, which has very strong repellent properties.

Q: I'm taking the liberty of contacting you because I've discovered that my wooden staircase is full of small holes and yellowish sawdust... I can't see any insects! My house is old and when you go down into the cellar the upstairs staircase is visible but the holes are on the steps seen from the house and seen from the cellar, so on both sides; they're small but very scattered and every day you can see yellowish sawdust... I don't know what to do I'm afraid it's going to spread everywhere ! I've had the house since 2006 and this is the first time it's happened but I think it could be from old firewood that I've brought into my cellar because when I put this firewood under my chimney, there was sawdust of the same colour ! I'd like some information on the problem and if you can give me a solution to make it go away !
A: Small holes in wood with sawdust, it's likely to be furniture beetles, which is the case because they reproduce in July and August when the weather is hot. If your wood is waxed, you'll have to treat hole by hole with a syringe !

Q: I'd like to kill capricorn beetle larvae in the pine planks that line the walls and ceilings of my home. Is this possible with your products ? How do you go about it ?
A: Apart from boron, no natural products are approved for treating wood any more, so you'll have to look into permethrin or our Margosa extract, which is an excellent natural repellent.

Q: Thank you for your quick reply. Well, on investigating further, there is one "big" hole, but several smaller ones here and there on the parquet and skirting boards. I hadn't seen them before, although I'm very observant, so I think they're relatively recent, but it's true that we've changed the layout of the furniture, so these parts have become less visible. I read your article on furniture beetles on your website. Do you recommend drilling the holes and injecting an insecticide ? Which of your products would be most suitable ? Organic turpentine wouldn't be enough, would it ?
A: You must not have read it properly. We drill holes when we inject into beams, but not into parquet. For furniture, insecticide is injected into existing holes using a syringe. For wooden floors, you can treat with a syringe, brush, roller or mop. I don't think woodworms like turpentine, but I'm not sure it kills them !

Q: I've just discovered capricorn beetles in the beams. What would you advise me to do to get rid of them ?
A: For the last 1 year, apart from boron, no natural product has been authorised for treating wood against wood-eating insects. However, margosa extract is an excellent insect repellent. The active ingredient in this treatment is based on Margosa oil (an oil native to India). Thanks to its broad spectrum and long duration of action, margosa is effective in most infested areas. Applied by spraying or injection. This organic insecticide blocks the development of larvae, disrupts foraging and sterilises adult insects. You can find margosa extract on our website, to be used diluted with 90% water.

Q: Hello, I've noticed the presence of capricorn beetles in my supply of firewood (oak logs). Is there a risk to the roof structure of the house, as I sometimes leave the basket of logs next to the fireplace between two fires ? Should I treat it, how and with what ?
A: I don't think there's anything to worry about for the framework of your house. Oak longhorn beetles can be seen between May and August, when they leave the wood to breed. So it's perfectly normal to see them at this time of year. The risk of contamination from your logs near the chimney to the roof structure of your house is very low. Whatever the case, you should remain vigilant and check from time to time for the presence of woodborers under your roof. As soon as they move in, the larvae start nibbling away at the wood. As far as control and prevention methods are concerned, I invite you to read our special report on this insect. You'll find plenty of answers there.

Q: Can you tell me how to eliminate the Capricorn beetle from my firewood stored outdoors ?
A: The difficulty with insecticide treatment in a pile of outdoor firewood is being able to apply the product. Because the logs are piled on top of each other, it's not easy to apply the products (whatever they are). The insecticide we sell is a contact insecticide. In other words, it will only work if you can bring it into contact with the insect, its larva or its egg. The other difficulty lies in the fact that this is a wood-eating insect. It is therefore mainly located inside the wood, as it feeds on it, and is therefore difficult to access. The 4J insecticide we sell has no wood protection function, unlike targeted wood treatment products (such as xylophene). On the other hand, it will get rid of longhorned beetles, as long as the treatment is carried out properly and methodically.
To be effective, the treatment must be applied to untreated wood. The solution, which is a little long and tedious but effective in killing longhorned beetles, consists of penetrating the insecticide into the holes made by these insects (syringe, spray, sponge, mop). When it comes to using our 4J insecticide, we know that it is effective against longhorn beetles. However, this natural pyrethrum-based product does not last long. It is therefore effective for rapid curative action, but not for preventive action. A second product will also give good results, but with a much longer residual effect. This is Margosa extract. Margosa's main property is to render all treated surfaces unfit for insect consumption. The insects must then either leave the treated area in search of food, or starve to death. Thanks to its broad spectrum and long duration of action, Margosa is effective in most infested areas. It can be applied by spraying or injection. Margosa blocks the development of larvae, disrupts the search for food and sterilises adult insects. Treatment to be carried out by spraying the wood and injecting it into holes at a concentration of 2% for preventive use and 4% for curative use. Use diluted with water as recommended.