GIMME SHELTER- Boring bees: More buzz than bite

Peter Warren
Virginia Cooperative Extension, Agriculture & Natural Resources agent
FILE PHOTO BY DAVE MCNAIR

Q: I have large bees buzzing around my house and boring holes in the wood.  What are these things, and what should I do about them?

A: If you are seeing large, black and yellow bees hovering around the eaves, decks, and wood siding of your home, you may have carpenter bees who are setting up housekeeping.  Although they can pollinate our flowers, carpenter bees can cause cosmetic and structural damage to wood as well. They can also be quite intimidating to homeowners and have the potential to inflict painful stings. 

Carpenter bees look similar to bumblebees, but differ in that they have a black, shiny tail end or abdomen while the bumblebee's abdomen is covered with hair.  Bumblebees nest in the ground, whereas carpenter bees tunnel into wood to lay their eggs. Common nesting sites include eaves, fascia boards, siding, wooden shake roofs, decks, and outdoor furniture. Bare, unpainted, or weathered softwoods are preferred, especially redwood, cedar, cypress, and pine. Painted and treated woods are less preferred, but they are not immune to attack. 

The tunnels are perfectly round and about the size of a dime. Coarse sawdust, the color of fresh cut wood, is often seen beneath the entry hole, and burrowing sounds may be heard within the wood. Female carpenter bees may excavate new tunnels or enlarge and reuse old ones. Serious damage can result when the same piece of wood is utilized for nesting year after year until it looks like Swiss cheese. Occasionally, several bees may use the same entrance hole and have individual branches off the main tunnel. If the same entrance hole is used for several years, tunnels may extend several feet in the wood.

Carpenter bees overwinter as adults in old nest tunnels and emerge in the spring, usually in April or May. After mating, the fertilized females excavate the tunnels, laying their eggs within a series of small cells, which are provisioned with pollen for the larvae to feed on. Males do not drill tunnels, but they will harass other bees and people who venture near the tunnels. The males, which can be distinguished from females by a whitish spot on the front of the face, do not sting. Females are capable of stinging, but rarely do so unless confined in your hand or are highly agitated. 

These adult bees die in a matter of weeks. The eggs hatch in a few days and the offspring complete their development in about 5 to 7 weeks. Adults begin to emerge in late summer. Although the bees remain active, feeding on pollen in the general area, they don't construct new tunnels.

The best time to control carpenter bees is before the tunnels are constructed.  Treating the entrance holes with an insecticidal spray or dust may substantially reduce nesting activity.  Leave the holes open for a few days after treatment to allow the bees to contact and distribute the insecticide throughout the nest galleries. Then plug the entrance hole with a piece of wooden dowel coated with wood glue, wood putty, or other sealant. This will protect against future use of the old nesting tunnels, as well as moisture intrusion and wood decay. Aerosol sprays sold for wasp or bee management are also effective and are often more convenient than dusts. 

However, since virtually any exposed wood on the house is subject to attack, it's difficult (and usually not practical or safe) to try to spray all of the possible sites where the bees might tunnel. Since these bees are not aggressive, and contribute to the pollination of our plants, it would be best to learn to live with them as much as possible.

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