Old House Borers | Pest ID Guide
Quick Facts About Old House Borers
The old house borer is a long-horned beetle whose larvae tunnel through softwood framing for years. Despite the name, it’s often found in newer homes, because eggs or larvae can come in with infested lumber during construction.- Size: Adults about 5/8 to 1 inch long
- Color: Grayish brown to black, with fine gray hairs
- Shape: Long, slightly flattened body with antennae about a third to half its body length
- What they eat: Softwoods such as pine and fir, especially seasoned framing lumber
- Life cycle: Larvae can feed inside wood for several years before emerging
- Key sign: Oval exit holes about 1/4 to 3/8 inch across
What Do Old House Borers Look Like?
Adults are rarely seen, and they live only a short time after emerging. Most homeowners discover the larvae’s damage instead.Key Identifying Features
- Two shiny knobs: A pair of raised, shiny bumps on the section just behind the head is the easiest way to recognize an adult
- Gray patches: Light gray hairs, often forming faint patches or bands on the wing covers
- Larvae: Cream-colored grubs up to about 1 1/4 inches long, with strong jaws
- Exit holes: Oval rather than round, which sets them apart from powderpost beetles
Old House Borers vs. Powderpost Beetles
Powderpost beetles leave small, round holes and fine powder. Old house borers leave larger oval holes, and their frass is packed tightly into the tunnels, mixed with tiny pellets. Compare with our powderpost beetle guide.
Signs of Old House Borers
- Clicking or rasping sounds: On warm days you may hear larvae chewing inside walls, beams, or joists
- Oval exit holes: About 1/4 to 3/8 inch wide in framing, joists, or trim
- Blistered wood surfaces: Rippled or blistered wood where tunnels run just under the surface
- Packed frass: Powder and pellets packed in the tunnels, sometimes spilling from holes
Health & Property Risks
Old house borers aren’t dangerous to people. The concern is structural: the larvae feed slowly but for years, and because they can reinfest the same softwood, damage can spread through attic rafters, floor joists, and wall framing over time.
Where to Look in Your Home
- Attic rafters and roof sheathing
- Crawl space joists and sill plates
- Wall studs and framing, especially where you hear clicking
- Stored pine lumber and softwood furniture
How to Prevent Old House Borers
- Inspect lumber: Check framing lumber, reclaimed wood, and firewood for holes before bringing it inside.
- Control moisture: Keep attics and crawl spaces ventilated and dry.
- Seal exposed wood: Finishes make it harder for females to lay eggs.
- Act on signs early: Treating a small area is far easier than replacing framing later.
When to Call a Professional
Call if you hear clicking in the walls or find oval exit holes in framing. A technician will confirm the insect and whether it’s active. Treatment may include borate products on exposed wood, replacing heavily damaged pieces, or fumigation for widespread infestations. See our beetle control services.
Frequently Asked Questions
What does an old house borer look like?
Adults are grayish-brown to black beetles about 5/8 to 1 inch long, with fine gray hairs and two shiny raised knobs just behind the head. Larvae are cream-colored grubs with strong jaws.
Why do I hear clicking in my walls?
A rasping or clicking sound on warm days can be old house borer larvae chewing through wood. Have it inspected, especially if you also find oval holes in framing.
Do old house borers only infest old houses?
No. Despite the name, they often turn up in newer homes, because larvae can be inside framing lumber when the house is built.
How long do old house borers live in wood?
The larvae can feed for several years before emerging as adults, and they can reinfest the same wood.
How are old house borers treated?
Common approaches include borate treatments on exposed wood, replacing damaged pieces, and fumigation for widespread activity. A professional inspection determines what’s needed.
