House Longhorn Beetle: How to Identify and Get Rid of It

The house longhorn beetle is one of the most destructive wood-boring pests in Central Europe. Its larvae can weaken the load-bearing structure of roof timbers and wooden beams over many years without being noticed. An infestation often goes undetected until serious damage has occurred.

This article explains how to identify house longhorn beetles. You’ll learn about effective treatment methods and when you can handle the problem yourself or need to call a professional.

How do I identify house longhorn beetles and woodworm?

Accurate identification is the first step. Don’t confuse the house longhorn beetle with less harmful species such as the common furniture beetle, often called “woodworm.” The adult beetle is 8 to 26 millimetres long, blackish-brown to black, and has long, thread-like antennae.

The larvae cause the damage. They can live in timber for up to ten years, eating their way through the inside. They leave behind a network of tunnels that can compromise the structural stability of the wood.

3 reliable signs of an infestation

1. Exit holes: After pupating, the beetles chew their way out of the wood, leaving oval holes 4 to 7 millimetres wide. Fresh holes have light-colored, unweathered edges.

2. Wood dust: You may find fine, flour-like wood dust beneath the holes. This can indicate active larvae. Tap the timber to make the dust easier to spot.

3. Gnawing sounds: In complete silence, you may hear a distinct nibbling or rasping sound coming from the timber. It sounds as if something is chewing on a small stick.

“A house longhorn beetle infestation is a silent form of destruction. The first signs, such as wood dust in the attic, often go unnoticed until the larvae have been active for years. That’s why regular inspections of roof structures are essential.”

For tools to inspect hard-to-reach areas, browse the accessories in our Power Tools category.

Why is the house longhorn beetle so dangerous?

The danger comes from the long-term damage and the way an infestation develops. A single female lays up to 400 eggs in cracks in the timber. The larvae begin eating their way into the wood as soon as they hatch.

They stay inside the timber throughout their development, so there may be no visible signs from the outside. The larvae prefer certain layers of wood. They eat the solid earlywood and leave the softer latewood behind.

Damage is often discovered only when the timber gives way or breaks underfoot. Repair costs can then be enormous. Early treatment can save money and protect the building’s structure.

How can I treat house longhorn beetles myself?

You can treat a localized infestation yourself if it affects non-load-bearing timber. Success depends on being thorough. Incomplete treatment can allow the infestation to return.

Step 1: Locate and contain the infestation

Mark all exit holes with chalk. Tap the surrounding timber systematically. A hollow sound may indicate areas that have been eaten away. Carefully drill small test holes to check the timber’s strength.

Step 2: Remove infested wood

Completely remove heavily infested sections of timber. Cut back into sound wood. Burn the infested material immediately or seal it in airtight packaging. Don’t store it on your property.

Step 3: Apply insecticide

Specialist products are available to treat the remaining, lightly infested timber. They can be injected deep into the exit holes and tunnels.

You’ll need specialist equipment for this work. Find practical accessories in our Garden + Outdoor range.

Which products help treat house longhorn beetles?

Choose products specifically designed to work against wood-boring insects such as the house longhorn beetle. Check that they’re approved for indoor use. We recommend these products:

: This concentrate is suitable for surface treatment and injection. It penetrates deep into the timber and provides long-lasting protection.

: Ideal for targeted treatment through exit holes. The practical syringe makes precise application easier.

: A ready-to-use spray for surfaces and hard-to-reach cracks. It leaves an effective protective film.

Find all the products mentioned in our Pest Control category.

When should I call a pest control professional?

DIY treatment may not be enough when the infestation covers a large area. If it affects load-bearing components, call a professional. You should also consult an expert if you’re unsure of the diagnosis.

A professional pest controller has access to powerful insecticides and specialist methods such as heat treatment or fumigation. They’ll create a treatment plan and carry out a follow-up inspection.

“Heat treatment is a highly effective, chemical-free method. The entire roof structure is heated to 55-60°C for several hours. This temperature kills all stages of the beetle without damaging the timber. However, the process requires considerable experience.”

How can I prevent a new infestation?

Prevention is the best protection. Treat newly installed softwood with a preventative wood preservative. This is especially important for roof structures, carports, and garden sheds.

Keep timber dry. Humidity below 18% inhibits larval development. Make sure attics are well ventilated. Remove old, infested timber from around your home.

For structural timber protection, including proper ventilation and roof overhangs, find materials in the Business Supplies section.

House Longhorn Beetle vs. Woodworm: What’s the Difference?

Many people confuse these two pests. The common furniture beetle, often called woodworm, is smaller and leaves round holes measuring 1-2 mm. Its infestation is usually more superficial and develops more slowly.

The house longhorn beetle is much more destructive and can cause severe damage more quickly. Confusing the two can have serious consequences because the treatments required differ in intensity.

: A comparison graphic shows the differences in hole shape, size, and typical signs of an infestation.

Conclusion: Act Quickly to Protect Your Property

An old house borer infestation is a serious problem. Do not ignore it. If you suspect an infestation, start a thorough inspection immediately. Decide whether to treat it yourself or call in a professional.

Invest in high-quality products and carry out the treatment thoroughly. The cost of proper pest control is always lower than the cost of structural repairs. This will help protect your home's value for years to come.

: An image shows a renovated, treated roof structure contrasted with a heavily infested beam.

Frequently Asked Questions

How can I tell if I have an old house borer infestation?

Look for small, oval exit holes (4-7 mm) in the wood, fine, flour-like wood dust underneath and audible gnawing sounds from the larvae. The larvae are cream-colored with a brown head and can grow up to 3 cm long. They are active from May to August.

Can I get rid of old house borers myself?

For small, localized infestations in non-load-bearing wood, DIY treatment with injection products may be possible. If load-bearing beams or roof structures are severely infested, consult a professional pest control specialist to prevent structural damage.

What type of wood do old house borers infest?

Old house borers prefer structural softwood, particularly spruce, fir and pine. They almost exclusively infest the sapwood and avoid the heartwood. Older buildings with untreated roof structures are especially at risk.

How long does it take for an egg to develop into a beetle?

Under Central European conditions, the larvae develop in wood over three to ten years, and in exceptional cases even longer. This long development period makes an infestation particularly difficult to detect, as it is often discovered only at a late stage.

Do old house borers also damage furniture?

Yes, old house borers can also infest wooden floors, loft cladding and old wooden furniture made from softwood. Take particular care with antiques. The risk is significantly lower for furniture made from hardwood.