Macomb and St. Clair Counties
Carpenter Bees
Appearance
Carpenter bees are blue-black to black in color with a green or purplish metallic sheen. They resemble large bumble bees but their abdomen is black, shiny and without hair. Their body size ranges from 3/4 to 1 inch long.
Behavior
Male carpenter bees have white markings and are the most visible of the species. They are aggressive and often hover in front of people who are near their nests. They are incapable of stinging and pose no threat though when encountered. The more passive female carpenter bee, however, is capable of inflicting a painful sting when she is provoked. Female carpenter bees can be identified by their unmarked, black heads.
Reproduction
Twice a year, in the spring and fall, homes can be invaded by carpenter bees. Adult carpenter bees emerge in the spring (April or May) after wintering in abandoned nest tunnels. At this time, females bore into timbers to create nest sites. They excavate new tunnels and clear out existing ones. After a nesting site has been excavated or cleared out, a female will provision the nest with a mass of pollen and nectar which she will then lay her eggs upon. Several females will share a common tunnel hole and nest in the same area. The gallery is then sealed with a mixture of saliva and wood pulp. The process of laying eggs is repeated until the female has completed a total of six brood galleries. In late summer, adolescent carpenter bees will emerge from the galleries and briefly visit flowers. They will then return to existing tunnels to hibernate for the winter.
Nesting
Carpenter bee holes appear about 1/2 inch in diameter and most often occur in areas protected from the weather. The holes they bore compromise wood's structural integrity, cause stains and attract woodpeckers. Check for entrance holes on common nesting areas such as structural timbers, eaves, window trim, fascia boards, siding, wooden shakes, decks and outdoor furniture. There will often be coarse sawdust on surfaces below the hole as carpenter bees do not actually ingest or feed on the wood itself. You may also observe woodpecker damage to the structure as these birds will attempt to reach larvae in the galleries. Another sign of an active infestation is the burrowing sound from the female carpenter bee which sounds like a vibration within the wooden surface.
Management
To control existing carpenter bee populations, each nest must be found and individually treated. To initially treat a discovered nest site, we strongly recommend an application of insecticide dust directly to the entrance tunnel. After treatment, the nest site should be left open for a period of two weeks before being fixed. This increases the chance of exposure to the pesticide for other carpenter bees visiting the nest. After the two week period, the nesting hole site must be plugged to insure complete eradication. For repairing the nest entrance hole, we suggest caulking with acrylic base Energy Seal. This product discourages further drilling and can accept stain to match the finish of your home. When pugging the hole, only the first 1/4 of an inch of the tunnel should be filled so that the residual insecticide can remain active within. Alternatively, a short piece of appropriately sized wooden dowel rod (slightly larger in diameter than the entrance hole) can be pre-cut and tapped flush into the hole with a hammer.