Identification
Carpenter bees resemble bumble bees. They are large, 3/4 to 1 inch long, heavy-bodied, blue-black to black colored with a green or purplish metallic sheen. The thorax is covered with bright yellow, orange or white hairs and the abdomen, especially on the top side, is black, shiny and bare without hairs. It is the males, with white markings on their head, that fly around aggressively, but they are harmless since they lack a stinger. Females have black heads, are docile and rarely sting. They have a dense brush of hairs on the hind legs whereas bumble bees have large pollen baskets and numerous, yellow hairs on the abdomen. Larvae are saclike, white and legless with brown, globular heads that bear small mouthparts. The pupal stage is passed in a silent cocoon.

Life Cycle and Habits
Both male and female carpenter bees overwinter as adults within their old nest tunnels. Adults emerge in the spring (April and early May) and mate. Females provision the tunnels or galleries with bee bread (mixture of pollen and regurgitated nectar), lay an egg on top of the mass and close the cell with chewed wood pulp. She excavates the gallery with her mandibles (mouthparts) at the rate of one inch in six days. The gallery has a clean-cut round entrance hole with sharp edges 3/8 to 1/2 inch wide (dime-sized) on the lateral wood surface. The gallery continues inward for one to two inches, then turns sharply at a 90 degree right angle running in the same direction as the wood grain for four to six inches or up to 10 feet long, if used by many bees. Damage from a pair of bees is slight, but if used by many bees over several years, damage can be extensive.

Each female may have six to eight sealed brood cells in a linear row in one gallery as she backs outward. Larvae develop on the pollen/nectar food mass provided, with the life cycle completed in 30 to 40 days. New adults chew through the cell partitions and emerge in late August. They collect and store pollen in the existing galleries, return to the tunnels to hibernate and mate the following spring. The previous year's adults die. They are not social insects and there is one generation per year.

Control Measures
Infestations are usually first detected by finding large amounts of sawdust droppings on the ground below the area being drilled or by observing bees going in and out of the round, circular holes in the wood affected. These bees attack all species of dried, seasoned wood, preferring softwoods such as cedar, redwood, cypress, pine and fir. Nail holes, exposed saw cuts and unpainted wood are attractive nesting sites. They may refurbish an existing tunnel instead of boring a new one or new tunnels may be constructed near old ones with infestations persisting for several years.

Prevention
Keep all exposed wood surfaces well painted (oil base or polyurethane) to reduce attack. Wood stains will not prevent damage. Aluminum, asbestos, asphalt, vinyl siding and similar non-wood materials will not be damaged. If practical, remove and replace damaged wood with chemical pressure-treated wood to discourage nest construction.

Insecticides
During the daytime, locate tunnel entrances and after dark, on a cool evening when carpenter bees are less active, treat directly into the nest entrance and on a wide area of adjacent wood surface. Do not plug the entrance since bees should be allowed to pass freely to distribute the insecticide within the holes. If tunnels are plugged before bees are killed, they may chew new openings elsewhere. Dust applications are usually more residual and effective than sprays due to the nature of the gallery construction. Even newly emerged bees will contact the dust when leaving the opening. After treatment, some wait until adult activity ceases or until autumn before sealing the hole with caulking compound or wood putty. This procedure reduces wood deterioration and possible future infestation. Be sure to wear protective clothing to avoid any stings during treatment.