Identification
The insect that reveals a water problem
Unlike the furniture beetle, which colonizes dry wood, the wharf borer develops only in wet wood. Finding a yellow-orange adult near a basement light in June or July is a warning: somewhere nearby, wood is in repeated contact with water.
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AElongated yellow-orange body
Adult 7 to 14 mm, soft flexible body, yellow-orange with the outer two thirds of the wing covers black. Very distinctive and easy to tell from other wood-boring beetles.
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BLong antennae
Thread-like antennae often reaching past half the body length. Males have longer antennae than females.
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CWhite larva in wet wood
White cylindrical larva, 20 to 25 mm when mature. Lives only in water-saturated or damp, decaying wood. A direct indicator of a moisture problem.
Adult
Emerges in summer (June to August) and lives a few weeks. Lays eggs in cracks in wet wood. Drawn to light at night, so it is often found dead near lamps or on window sills.
Life cycle
HOLOMETABOLOUS · 4 STAGES · 2 TO 3 YEARSLaid in cracks in water-saturated wood. Needs very high moisture content to hatch.
Bores tunnels through wet or submerged wood and can turn sound wood into a hollow fibrous mass. This is the destructive stage.
Rests just under the surface of the wood. The adult bores a 4 to 6 mm hole to get out, usually in June to August.
Flies at night toward light and breeds within its first week. Adults always mean a source of wet wood nearby.
Do not confuse it with
The wharf borer is sometimes mistaken for the furniture beetle or a longhorn beetle. Its habitat (wet wood), its colouring and its life cycle set it clearly apart.
Longhorn beetle
Very long antennae, wood-boring larvae, large oval exit holes.
Common furniture beetle
Small brown beetle leaving round 1 to 2 mm holes in dry wood.
Signs of activity
Adults found dead or alive
Yellow-orange adults 7 to 14 mm, mostly in June to August. Found near lamps, on basement window ledges or on the stairs. A direct sign of infestation.
Round exit holes 4 to 6 mm
Large round holes in basement wood, rim joists or framing in contact with moisture. The wood around them sounds hollow.
Soft, spongy wood
Infested wet wood turns fibrous and crumbles easily under finger pressure. Tunnels are packed with damp shavings and droppings.
Any wharf borer adult found in a basement in summer should trigger a systematic search for the moisture source. Killing the insect settles nothing: as long as the wood stays wet, the cycle continues.
Treatment
Borate treatment for wet wood
- 1 L Borate solution (boric acid spray) Soaks into wet wood and kills the larvae; works as both a fungicide and an insecticide
- Find and fix the moisture source (leak, condensation, seepage). Dry the wood for two weeks with a dehumidifier. Spray the borate solution on every face of the infested wood. Let it soak in for 7 days before sealing or replacing.
No insecticide holds up on wood that stays wet. The first step is always to bring the wood below 19% moisture content, before any chemical treatment.
Detecting an active infestation
Confirm the insect, then find the water
From June to August, look for yellow-orange adults near basement lights or on the basement stairs. A single adult confirms wet wood nearby.
Go over every rim joist, low sill and piece of wood touching concrete, soil or plumbing with an awl. Infested wood is soft and spongy and gives way under light pressure.
Measure the wood with a moisture meter: above 19% the conditions suit the wharf borer. Identify where the water comes from before treating anything.
Prevention
- End the wood-to-water contact
No structural wood should sit in prolonged contact with water or damp soil. Install flashing, lay a vapour barrier in the crawl space and drain around the foundation.
ZONE 1 · BASEMENT
Frequently asked questions
What is the wharf borer?
An elongated yellow-orange and black beetle drawn to light. It is often mistaken for a longhorn beetle, and it develops only in wet wood.
Is it dangerous?
Not to people: it does not sting and it does not attack sound dry wood. What matters is what it signals, namely wood soaked with water.
Why do I see them indoors?
Adults emerge in summer from wet wood in the basement or crawl space and head for the lights, so they turn up near lamps and windows.
How do I get rid of them?
Fix the water problem and dry the wood, then treat or replace the affected pieces. An exterminator can confirm the species and locate the source.