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Michigan State University Extension
Home Maintenance And Repair - 01500558
06/24/03

Carpenter Bee



Two species of Xylocopa, or carpenter bees, occur in the eastern U.S. Xylocopa virginica is found from Maine to Wisconsin and south to florida and Texas. In Michigan it appears to be restricted to the southern half of the state. Xylocopa micans Lepeleter occurs in the southeastern states. Carpenter bees are widespread in their distribution, but are seldom abundant in any given locality.

The adult carpenter bee resembles the common bumble bee. Carpenter bees are large (20-30mm), robust, and with a shiny, bluish-black abdomen. Bumble bees, on the other hand, have a hairy abdomen that is mostly yellow.

Adults excavate nests in wood. Softwoods (pine, redwood, fir, cedar, and spruce) are preferred, but they have been seen nesting in hardwoods (willow and oak). A "nest" consists of a round entrance hole (0.5 inch diameter by 1.5 - 2 inches deep) and a system of tunnels oriented along the grain of the wood. Tunnels range in length from a half foot to several feet (after years of use). The bees cut one half inch per day to open the entrance hole, and then move at a faster pace as they cut the tunnels with the grain.

Nests are located in porches, eaves, fascia boards, garages, sheds, carports, fences, window trim, lamp posts, and other wood objects. Nests are most likely to be southern or eastern in aspect. They tend to avoid wood that is painted, whitewashed or covered with bark. Juvenile (unmated) adults of both sexes overwinter in the tunnels. They become active when temperatures reach the 70's in the spring. Mating, accompanied by a strange "bobbing dance" by the male, occurs in April.

The bees clean and enlarge the nest. They seem to prefer this to establishing new nests. Therefore, nests may be used by many generations of bees. Some nests have been known to have been in use for 14 years. The females prepare a series of brood cells in the tunnels, providing each with food ("bee bread" - a mixture of pollen and nectar), an egg, and a partition of chewed wood. Most females produce 6 to 8 young. The larvae develop from May to August, emerging in September. The oldest bee, developing at the end of the tunnel, emerges first and must cut through all the partitions and crawl over the other developing bees. There is only one generation per year.

There are two principle concerns about the activities of carpenter bees. One concern is over the possibility of stings. However, this is actually of minor consequence since the females (males can't sting) are very hesitant to sting, and in fact must be held to provoke a sting. In addition, they are mild stings.

The second concern deals with wood damage. It is generally more of an aesthetic problem since they rarely nest in structural timbers. Damage is most severe in trim and decorative wood on the exterior of the building. Other concerns include stains of excreta, the buzzing flight of the adults, the noise of nest construction, and the attraction of (hungry) woodpeckers.

Carpenter bees are not particularly important as pollinators. In addition to woodpeckers there are two species of bee flies (Diptera: Bombyliidae) that are natural enemies of the carpenter bee. The flies deposit their eggs in the entrance of the tunnel and the maggots parasitize the bee larvae.

Carpenter bees are best controlled by placing ready to use diazinon, or contact sprays of pyrethroids in the tunnels. After thoroughly treating, plug the entrance with a dowel of the appropriate size. It may be helpful to treat the sites used, or most likely to be used, with one of the residual insecticides mentioned previously. This should be done in the spring prior to the time when the bees begin nest construction.

For a complete listing of suggested control options for all home, yard and garden insect pests contact your local Extension Service, found under local government in the phone book.

Read and follow instructions on the pesticide label. Heed all warnings. Check with your physician if you have any concerns regarding your personal health risk.

References

Revised by Tom Ellis, M.S., Department of Entomology

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