**Old House Borers** (*Hylotrupes bajulus*) are long-horned beetles whose larvae are one of the most destructive insect pests of seasoned softwood timber (especially pine, fir, and spruce) in structures. The conflict is severe, hidden, and progressive structural damage: the larvae tunnel deep into the wood, consuming cellulose, weakening structural support beams, and making the wood vulnerable to fracture. The damage can go undetected for years, often surfacing only when the structure is visibly compromised or the distinctive sound of chewing is heard.
Taxonomy and Classification
Old House Borers belong to the order Coleoptera (Beetles), family Cerambycidae (Long-horned Beetles). They undergo complete metamorphosis. The larval stage is extremely long-lived, lasting 2 to 15 years, during which time it feeds continuously within the wood structure.
Physical Description
Adult Beetles are 3/4 to 1 inch long.
- **Adult (Key ID):** Black or brown, somewhat flattened beetle with long antennae and two shiny black “tubercles” that resemble eyes on the thorax.
- **Larva (Key ID):** Large, white, segmented grub with a slightly enlarged thorax, found deep inside the wood.
- **Damage Sign (Key ID):**
- **Oval Exit Holes:** 1/4 to 3/8 inch diameter, oval holes on the surface, indicating the adult has emerged.
- **Frass (Bore Dust):** Fine, powdery frass that feels gritty or sawdust-like (often spilling out of the exit hole).
- **Chewing Sound:** A distinct, scraping, or rhythmic sound of chewing heard coming from within infested timbers (often noticeable on warm days).
- **Conflict:** Severe, progressive structural failure.
Distribution and Habitat
Old House Borers are found globally, concentrated in areas using softwood lumber for construction. Their habitat is the seasoned softwood components of structures, particularly attics, roof trusses, floor joists, and subflooring.
Behavior and Conflict
The conflict is its slow, hidden, and persistent nature.
- **Hidden Infestation:** Most damage is internal, with the structural integrity of the wood (especially the sapwood) being hollowed out before external evidence (the exit hole) appears.
- **Long Life Cycle:** The larval stage can last many years, meaning the damage is continuous and severe, eventually requiring expensive replacement of infested timbers.
- **Moisture Preference:** They typically prefer seasoned wood but are often found in wood with slightly elevated moisture content, common in attics with poor ventilation.
Management and Prevention
Control requires professional inspection and treatment of infested wood.
- Use pressure-treated or naturally resistant lumber in construction (especially in high-moisture areas).
- Ensure proper attic and crawlspace ventilation to reduce moisture.
- **Fumigation:** For severe, widespread, or inaccessible infestations, the entire structure may need to be tented and fumigated.
- **Targeted Treatment:** Apply a persistent, residual insecticide (liquid or foam) directly to the surface of infested wood members and inject it into exit/frass holes to kill internal larvae.
- Remove and replace heavily damaged structural members if their integrity is compromised.
Conservation and Research
Old House Borers are managed as high-priority structural pests. Research focuses on improving non-toxic and localized treatment methods (like heat or cold application) and developing faster, more sensitive acoustic detection tools for internal larval activity.