Carpenter bees are large (3/4 to 1 inch long), heavy-bodied insects. Their blue-black metallic bodies will have some yellow or orange hair. They resemble bumble bees, but can be distinguished by their shiny, black, hairless abdomens. The abdomen of the bumble bee is yellow and hairy. Bumble bees also have large pollen baskets on their hind legs.
In the spring, carpenter bees become a nuisance as they fly erratically close to homes and other buildings. Males hover like humming birds, waiting for females to emerge so they can mate. If the males are disturbed, they may hover or buzz around a person's head. Only the females sting, and then only if molested. After the mating season, most of the summer is spent loitering around the nest or nearby flowers.
In addition to being a nuisance, they also bore into seasoned wood, particularly soft woods such as cedar, redwood, pine, and fir. Damage may occur to soft or weathered wood on porches, decks, shed ceilings, railings, overhead trim, porch, furniture, dead tree limbs, fence posts, wooden shingles, wood siding, window sills, wood doors, etc. Female bees bore circular holes, about 1/2-inch wide, into the wood at right angles to the surface for about an inch. Then they turn sharply excavating the direction of the wood grain for 4 to 6 inches.
Structural damage caused by one or two carpenter bees is slight. However, tunnels may be used again and lengthened by other subsequent broods. The activity of numerous bees over a period of years is certain to cause some structural damage.
Carpenter bees overwinter in wood as young adults. The tunnels are made by the females. Those bees that survive the winter mate in the spring (April to June) and then begin preparation for the next brood.