This article explains how to identify house longhorn beetles (Hylotrupes bajulus), where they are found in the UK, how to prevent them, and how to get rid of them in homes and buildings.
In the UK, this pest is most commonly referred to as the house longhorn beetle, but it is also known as the old house borer, timber beetle, or woodboring beetle, depending on the context.
What do house longhorn beetles look like?
Adult house longhorn beetles are dark brown to black and typically 8–25 mm long. They have a flattened, elongated body and distinctive antennae that can be up to half the length of their body. Two black, shiny eye-like spots on their thorax help distinguish them from other beetles.
The larvae are creamy white, slightly curved, and can reach up to 30 mm in length. It is the larvae—not the adults—that cause damage, as they tunnel through softwood timber while feeding.
Where are house longhorn beetles found in the UK?
In the UK, the house longhorn beetle is primarily found in southern England, particularly in areas with a warmer climate and older housing stock. However, they can occur elsewhere, especially where imported or untreated timber is used.
Common locations include:
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Roof timbers and attic spaces in houses
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Softwood structural elements such as joists and rafters
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Behind wooden panelling and under floorboards
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Older properties built with untreated or poorly ventilated timber
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Occasionally in timber stored in outbuildings or garages
The beetle prefers softwoods like pine, fir, and spruce, especially when the timber is dry and aged.
How can you identify an infestation of house longhorn beetles?
Early detection is often difficult, as the larvae can remain hidden within wood for many years.
Key signs of infestation:
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Oval exit holes in wood, usually 6–10 mm in diameter
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Fine, powdery dust (frass) found near or beneath timber
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Weakened beams or floorboards that sound hollow when tapped
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Scratching or rasping noises from inside walls or roof timbers (larval activity)
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Adult beetles appearing indoors, especially during summer
The presence of exit holes alone does not confirm an active infestation—only that adult beetles have emerged in the past.
Where do house longhorn beetles live and reproduce?
The beetle lays its eggs in cracks or crevices in bare or unpainted timber. Once the eggs hatch, the larvae bore into the wood and feed for several years.
They most commonly inhabit:
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Roof timbers such as rafters and battens
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Floor joists, beams, and timber lintels
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Wood stored in dry, undisturbed areas
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Poorly ventilated roof spaces with exposed softwood
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Timber used in construction that was previously untreated
Reproduction and development are favoured by warm, dry conditions and poorly ventilated environments.
What is the life cycle of the house longhorn beetle?
The house longhorn beetle has a lengthy and destructive life cycle:
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Eggs – Laid in surface cracks of softwood timber
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Larvae – Bore deep into the wood and feed for 3–10 years, depending on temperature and moisture
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Pupae – Form near the surface of the timber and remain for several weeks
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Adults – Emerge through exit holes, mate, and die shortly after
In heated buildings, the life cycle may be shorter, while in cooler environments it can last much longer.
How can you prevent house longhorn beetles?
Use treated timber
Ensure all structural softwood used in construction or repairs is properly treated with insecticidal preservatives.
Maintain good ventilation
Ensure lofts and roof spaces are well ventilated to reduce humidity, making conditions less favourable for larval development.
Avoid using untreated reclaimed timber
Do not install reclaimed wood unless it has been professionally treated or kiln-dried to kill any pests present.
Paint or seal exposed wood
Coating vulnerable timber surfaces helps prevent egg-laying by adult beetles.
Regularly inspect at-risk areas
Carry out periodic checks in lofts, attics, and timber structures, especially in older properties in southern England.
How do you get rid of house longhorn beetles?
Professional assessment
Have a qualified timber treatment specialist inspect the property to confirm active infestation.
Remove and replace damaged timber
Severely infested wood should be removed and replaced with treated timber.
Apply insecticidal treatment
Specialist wood preservatives are injected or applied to the surface to penetrate and kill larvae inside the wood.
Heat treatment (in some cases)
Raising timber temperature to above 55°C can destroy all life stages of the beetle. This is a controlled, professional process.
Structural fumigation (rare)
In extreme infestations, full fumigation may be recommended, though it is rarely used in the UK due to cost and complexity.
Are house longhorn beetles harmful to people or pets?
House longhorn beetles are not dangerous to humans or pets. They do not bite, sting, or spread disease. The real threat is structural, as they can cause serious long-term damage to timber in buildings, weakening roof supports, joists, and flooring.
If left untreated, infestations can result in costly repairs and, in severe cases, compromise the safety of the structure.
In which parts of the UK are house longhorn beetles most common?
House longhorn beetles are most commonly found in:
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Southern and south-eastern England
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Areas with older housing stock, especially from the early to mid-20th century
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Properties with poor roof ventilation or untreated structural timber
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Buildings that used imported or reclaimed timber without proper treatment
The species is more prevalent in warmer areas of the UK, but infestations have been recorded across a wider range, particularly where softwood construction is common. Vigilance, proper timber treatment, and routine inspection are essential in preventing long-term damage from house longhorn beetles.