How to Bug Proof Your Home: Carpenter Bees

Pest Management In and Around Structures May 20, 2009 Print Friendly and PDF


Carpenter bees resemble bumble bees. They are large, 3/4 to 1 inch long, heavy-bodied, blue-black to black colored with a green or purplish metallic sheen. Carpenter bees are solitary bees. That is, they do not live in a hive like honey bees. They do, however, tend to accumulate in certain areas.

Although technically wood-boring insects, they are not really considered a true structural pest. They will not spread throughout the structure, but they will utilize any outside wood that is not painted or finished. Carpenter bees get their name from their ability to drill through wood and nest in the hole. Their drilling creates a near perfect hole, approximately 1/4 inch in diameter. The hole is usually located on the underside of the wood surface, including siding, decks, overhangs, fence posts and window frames. Although the hole appears to be only an inch or two deep, it rarely ends there.

Along with the coarse frass (sawdust and insect droppings) found underneath the nest entrance, there are usually dirty-yellow streaks of fecal matter staining the wood below the hole. If you are near a nest you will likely be buzzed by the male carpenter bee on guard. He is loud and aggressive, but does not have the ability to sting you. The female can sting but she is normally very docile. A single pair (male and female) occupies each nest.


  1. Try to paint everything made of wood, even the areas you don’t see, such as under windowsills and under banisters and railings. Use a good exterior primer, two coats; follow up with at least one coat of finish.
  2. Covering wooden components with aluminum sheeting will work only if done correctly. This means that you must eliminate any spaces where the bees will find the wood. They can squeeze through incredibly small places, so you have to be very thorough. Spaces or holes 1/4 inch or larger will let these bees through.
  3. You should use pressure-treated wood in any outdoor project such as decks and playhouses. Pressure-treated wood needs no paint, but can be painted if you wish.
  4. Cedar does offer some protection, but even cedar is attacked if the conditions are right.

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.