Carpenter bees are large (1/2- to 1-inch long), robust insects that look like bumble bees. They differ by having a bare, shiny black abdomen compared to bumble bees, which have a hairy abdomen with some yellow markings. Male carpenter bees, identified by the bright yellow spot in the middle of the head, are aggressive but quite harmless since they lack stingers. Females can sting if molested.
Adult over winter in galleries, emerging in the spring to mate. The female prepares a nest by excavating a new site or more frequently by cleaning out and expanding an existing tunnel. After the nest is ready, she places a mass of pollen mixed with nectar in the blind end of the tunnel, lays an egg on it, and builds a partition of chewed wood pulp to form a brood cell. Six to eight brood cells are constructed in each tunnel. The bee larvae develop on the pollen and emerge as adults 30 to 40 days later, usually in late summer. There is one generation per year.
Carpenter bees actually bore holes in wood to create a tunnel in which to raise their young. Carpenter bees are not social insects, i.e., they do not live in nests or colonies like yellow jackets and honey bees. The entry hole is 3/8 to ½-inch in diameter and initially about 6-inches long; in subsequent years, however, this maybe extended to more than ten feet. The initial opening is straight into the wood, then the gallery typically makes an abrupt right angle and follows the grain of the wood and parallel to the outer surface. Entry holes are usually located in will-lit and sheltered areas, such as headers, roof eaves, porch ceilings, fascia boards, decks, doors, and window sills. Soft wood, such as California redwood, cedar, white pine, and poplar is preferred for next building.