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Pest evidence guide

Carpenter Bee Holes: How to Identify It

Perfectly round holes, 10mm in diameter, in untreated wood. Caused by carpenter bees excavating tunnels for nests.

DamageMedium riskUpdated July 2026

Photo guidance

We only show reference photos when the image clearly matches this evidence type. Use the checklist below to compare what you found.

How to use this evidence

A clear photo can support a visual comparison with known pest evidence.

A photo alone cannot confirm the source or extent of an infestation. Check for matching physical evidence nearby.

What you found

Carpenter bee holes are perfectly round, approximately 10mm in diameter, drilled into untreated or weathered wood. Unlike carpenter ants, carpenter bees do not eat wood — they excavate tunnels to lay eggs. The holes are typically found on the underside of deck rails, eaves, fascia boards, and outdoor furniture.

Common places to check

  • Inspect deck rails and nearby hiding spots for matching evidence.
  • Inspect eaves and nearby hiding spots for matching evidence.
  • Inspect fascia boards and nearby hiding spots for matching evidence.
  • Inspect outdoor furniture and nearby hiding spots for matching evidence.
  • Inspect fence posts and nearby hiding spots for matching evidence.
  • Inspect window trim and nearby hiding spots for matching evidence.

How to identify it

Perfectly round entrance holes, approximately 10mm (3/8 inch) in diameter
Holes are often on the underside or protected surfaces of wood
Sawdust-like frass may accumulate directly below the hole
You may hear buzzing or chewing sounds from inside the wood
Multiple holes in the same area indicate repeated nesting

What it may indicate

Structural context

Repeated nesting in the same wood over years can cause significant structural weakness. Tunnels can extend 15-30cm into the wood.

Property context

Damages decks, eaves, fascia boards, and outdoor furniture. Unsightly holes reduce property aesthetics.

Infestation context

New generations return to the same nesting sites year after year, compounding damage over time.

Recommended actions

  1. 1Fill existing holes with wood putty or steel wool after bees have emerged (late summer/fall)
  2. 2Paint or stain all exposed wood surfaces (bees prefer untreated wood)
  3. 3Apply insecticidal dust into active holes in spring
  4. 4Hang carpenter bee traps near affected areas
  5. 5Replace heavily damaged wood with treated or composite materials

Prevention and monitoring

Paint or stain all exposed wood surfaces (bees strongly prefer bare wood)
Fill existing holes with wood putty and paint over them
Use treated lumber, composite materials, or hardwoods for outdoor projects
Install carpenter bee traps in early spring before nesting begins
Inspect decks, eaves, and fascia boards annually for new holes

Professional options

  • Professional insecticidal dust application to active tunnels
  • Structural assessment of wood damage extent
  • Replacement recommendations for compromised structural wood
  • Preventative treatment program for large structures