Carpenter Bees

EN020 (3/01)

Gale E. Ridge
Department of Entomology
The Connecticut Agricultural Experiment Station
123 Huntington Street
P.O. Box 1106
New Haven, CT 06504-1106

Telephone: (203) 974-8600 Fax: (203) 974-8502
Email: Gale.Ridge@ct.gov 

Adult carpenter bees (Xylocopa spp.) are considered a nuisance because they excavate tunnels into the wood of buildings. Repeated years of infestation can cause serious structural damage. Carpenter bees have a worldwide distribution. There are seven species found in the United States of America.

Carpenter bees and bumble bees look very similar but are quite different in their habits of behavior, size and on close examination, appearance. Carpenter bees are not social and excavate galleries in wood, while bumble bees live in small colonies of up to 400 individuals in the ground. Carpenter bees are much bigger than bumble bees being ¾ to 1 inch in length. They have hairless shiny black abdomens, while bumble bees have yellow and black hairy abdomens. Female bumble bees and carpenter bees can sting. Male carpenter bees, because they have no stingers, can not sting and so are harmless.

In Connecticut, May and June are the months when carpenter bees are seen actively flying around buildings. Males fly erratically, and can hover near to people causing fright. This is territorial behavior and the erratic flight patterns are for display purposes only. The females are less active and spend much of their time chewing holes into exterior wood surfaces. The holes are perfectly round and the size of a dime. Common tunneling sites include eaves, fascia boards, porches, decks, wood railings, fence posts, wood shingles, window and door trim, outdoor furniture, telephone poles, dead tree limbs and any other site where there is exposed wood. Tunnels tend to be located on the sunny side of a building. Carpenter bees prefer exposed unpainted softwoods such as redwood, cedar, cypress, fir, spruce and pine. The excavating female bee will bore straight into the wood for approximately one inch. She then turns 90º following the grain of the wood and chews a tunnel up to 10 inches long. The wood is not eaten but expelled from the tunnel as fine sawdust. It takes a female about 6 days to chew one inch of tunnel. Females are known to refurbish old tunnels from previous infestations, expanding them with more galleries.

Once excavation is complete, the female makes a series of cells starting at the deepest point of the tunnel and backs out. She stocks each cell with a mixture of pollen and nectar called "bee bread" and lays an egg onto the food. Each cell is sealed with chewed wood pulp. A female may produce six to eight brood cells, before she dies.

After hatching, each larva feeds on the pollen and nectar until it matures in late August. Due to the fact that the cells are lined up inside a tunnel, adults emerge in the reverse order of the eggs being laid. The first adult to emerge is from the cell closest to the entrance of the tunnel, while the deepest cell will be the last to produce an adult.

New adults emerge by chewing their way through the cell partitions. During late summer and fall, some adults may disperse to new locations, while others collect and store pollen in their natal tunnels in preparation for over wintering. When the weather becomes cold, the adult bees go into hibernation until the following spring when they leave to mate. They become active when temperatures reach 70ºF. There is one generation a year.

Exposed non-painted wood, nail holes and saw cuts are attractive sites to carpenter bees. They can be deterred by painting wood with oil or polyurethane based paints. Wood stains are not effective against carpenter bees. Pressure treated wood can have some deterrent effects. In certain situations, covering exposed wood with aluminum, vinyl, asphalt or other similar non-wood materials can stop carpenter bee activity.

When a female is observed tunneling, a homeowner may attempt to control the problem. At night, female carpenter bees often rest in the tunnels they are constructing. This is the time to treat the tunnels, using an aerosol spray of a pyrethrum-based or similar product labeled for bee and wasp control.

Inject into the entrance of each tunnel a steam of the spray. Be cautious about possible back splash while treating the tunnel. Consider wearing protective cloths and eyewear. After treatment, cover the hole with some tape, such as duct tape for 24 hours. This contains the pesticide. Remove the tape and watch for any further activity. Repeat the procedure if the female is not killed. Occasionally, a female might rest over night on foliage, not far from her tunnel. This makes control more difficult.

Pesticide residual dust treatments can also be effective. Treat tunnels at night. As the bees move around, they might encounter the dust. It may be absorbed through the integument (outer skin) or in grooming, be injested. Dusts available are Perma-Dust (boric-acid), Sevin (carbaryl), Microcare (pyrethrin), Ficam (bendicarb).

Demand CS (lambda-cyhalothrin) and Cynoff WP (cypermethrin), both restricted pesticides can be used as repellents. A licensed pest control operator might apply either formulations to susceptible wood in early May for protection during much of the insect’s breeding period.

Labeled pesticides for use by homeowners and by licensed pest control operators are listed below.

Liquid sprays of Pyrethrin, Resmethrin, Sevin (carbaryl), Baygon (propoxur), and Diazinon. Read the manufacturers’ recommendations carefully before treating for carpenter bees.

Astro, Flee, Dragnet, Prelude or Torpedo (permethrin); Saga (tralomethrin); Cynoff, Cyper-Active, Demon (cypermethrin); Tribute (fenvalerate); Ficam Plus (bendiocarb and pyrethrin); Suspend (deltamethrin); Optem, Tempo (cyfluthrin); Dursban, Duration, Empire, Engage, Tenure(chlorpyrifos); Drione dust (silica jell/powdered pyrethrum; and Biflex (bifenthrin).

Once the carpenter bees have been controlled, use wood putty or like materials to seal the entrance holes. This will discourage future activity and possible wood decay.

Summary

Adult carpenter bees (Xylocopa spp.) are considered a nuisance because they excavate tunnels into the wood of buildings. Repeated years of infestation can cause serious structural damage. Carpenter bees have a worldwide distribution. There are seven species found in the United States of America.