Carpenter Bees (Xylocopa spp.)

-- A large, colorful, wood-boring bee --

Summary: Wood boring carpenter bees resemble bumble bees but these large bees excavate tunnels in wood to make a nest whereas bumble bees nest in soil. This nest building can damage wood trim, doors, and so forth. While wood boring carpenter bee damage is usually minor it should still be repaired as soon as possible to prevent water infiltration and rot.

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Jack DeAngelis, ext. entomologist (ret.) revised: 11/2018

Carpenter bee identification

Carpenter bees are large, colorful wood-boring bees that look somewhat like bumble bees [see picture of carpenter bee]. The difference is that bumble bees are uniformly covered with dense hairs whereas carpenter bees have the upper surface of the abdomen bare and shiny black (see What is a Bumble Bee?).

Carpenter bees occasionally construct nests in exterior structural or decorative wood such as siding, fascia boards, trim, and log homes. A round hole (~1/2" diameter) is chewed in the wood surface then a tunnel is bored, usually at 90 degrees to the entrance.

a wood boring carpenter bee

carpenter bee - a bumble bee look-a-like; photo by USDA/ARS.

carpenter bee tunnels bored in trim wood

Carpenter bee nest (tunnels). Original drawing from Wood-Inhabiting Insects in Houses by Harry B. Moore, 1979. USDA, Forest Service and HUD.

Carpenter bee nest tunnels

The tunnels that are constructed by the female bee may be re-used year after year, and extended each year. This tunneling eventually weakens the wood and entrance holes can allow water to get in and cause wood to rot. Entry holes on the surface are round and generally about 1/2" in diameter. Once the tunnels are excavated nests are provisioned with pollen which feeds developing larvae.

Preventing carpenter bee damage

Most intact wood finishes like paint will prevent damage from these bees. Unfinished wood surfaces are far more likely to be attacked than finished wood. Paint works better than stain to resist carpenter bee attack but even just stain is better than no finish at all. The bottom line is that heavier, thicker finishes are best. Softer wood such as pine or fir is generally selected by female bees for tunnel-making and surfaces in direct sunlight, as compared to shaded areas, are preferred for nesting sites.

Repairing damage caused by bees

Carpenter bee holes should be repaired to prevent bees from enlarging the tunnels year after year. If left open these entrance holes may allow water and rot fungi to attack wood which in the long run will cause more damage than the bees themselves.

To repair carpenter bee damage you'll need some exterior caulk, 3/8"-1/2" wood plugs, and an insecticide to treat the holes and tunnels. Several insecticides are available for this application. EcoPCO WP-X is a botanical insecticide that is effective and there are also conventional insecticides approved for this use as well, see this site for details (DoMyOwn.com).Since approved usage can change be sure to check the package label for carpenter bees.

Treat around the entrance holes with insecticide at the proper rate (see label instructions) using a pump sprayer or duster, allow to dry if necessary then seal the hole with caulk and/or a plug, then finish to match the existing surface. You can also dust (puff) one of the dry insecticides into the tunnel prior to installing the plug.

Supplies

Professional-level pest control supplies are generally not available in home and garden stores but can be found at DoMyOwn, our affiliate.

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