Carpenter Bees

It sometimes happens in the late spring and early summer that homeowners will notice very large, blackish bees hovering around the outside of their home, especially if the home has a wood exterior. The appearance of these large, round bees is often accompanied by the discovery of many small , perfectly round holes in the side of the house, almost as if somebody had come by at night with a power drill and drilled holes in the side of the house. This is the work of the carpenter bee, one of the most interesting members of the bee family.

What does a carpenter bee look like?

Carpenter bees resemble bumble bees, except that the backside of their abdomen is hairless, shiny and black. Male carpenter bees are orange to yellow in color, but females are always completely black.

Another way to identify a carpenter bee is by the location where it is sighted. Carpenter bees always nest in wood; most homeowners who have a problem with carpenter bees will notice them hovering around the outside of the house. Bumble bees, on the other hand, nest in the ground and do not tend to hover around the exterior of the home. Male carpenter bees are quite aggressive and are known for “buzzing” the heads of humans (flying aggressively around people in very close proximity to the head). This behavior can be unnerving. However, it is all quite harmless, as the male carpenter bee is not equipped with a stinger. This “buzzing” is believed to be a form of intimidation used by males to frighten potential threats away from nearby nesting areas. The black females, on the other hand, are equipped with a stinger and can deliver a very painful sting. Fortunately females are not aggressive and do not sting unless molested.

Also, unlike other sorts of bees, carpenter bees are not social. Each carpenter bee is solitary and dig their own, individual nests. Therefore carpenter bees will not swarm and are usually seen alone. If the bees you are seeing are swarming, they are not carpenter bees.

Life Cycle

Young adult male and female carpenter bees hibernate in their nests during the winter. They mate in the spring, during which time they clean out and enlarge the old tunnels or excavate new ones as brood chambers for their young. Each chamber is provisioned with “bee bread”, a mixture of pollen and regurgitated nectar, which serves as food for the larvae. An egg is deposited on the food supply and each chamber is sealed off. There are typically 6 to 8 chambers created by the female. The larvae that hatch from the eggs complete their development and pupate. Newly developed adult carpenter bees emerge in August, feed on nectar and return to the tunnels to over-winter.

Carpenter bee damage and treatment

Carpenter bee damage comes from their nesting habits. Unlike honey bees who make hives or bumble bees who live in the ground, carpenter bees make their nests in wood. In nature, these nests would be made in softwood trees, such as redwood, cedar, cypress and pine. Because these woods are often used in home construction, homes with wooden exteriors attract carpenter bees. Common nesting sites include eaves, window trim, facia boards, siding, wooden shakes, decks and outdoor furniture. Bare, unpainted or weathered softwoods are preferred; painted or treated wood is less susceptible.

The carpenter bee will begin a nest in the wood siding of a home by excavating an entry point in the wood with their powerful jaws. Unlike termites, carpenter bees do not eat the wood they excavate; sawdust from excavated wood will be pushed out the resulting hole. The hole will always be very close to 1/2 inch in diameter. The bee will dig straight back for about an inch and then suddenly turn at a 90 degree angle and continue drilling for several more inches. The end of this tunnel will serve as a chamber for the female carpenter bee to lay her eggs in (a single nest may contain 6 to 8 chambers). The construction of the nest at a 90 degree angle ensures that the egg chamber cannot be reached by birds or other predators sticking their noses into the nest opening. This also means that you cannot destroy the carpenter bee hive by just jabbing around in the hole with a long object.

While one carpenter bee hole is not that big of a problem, the larvae that hatch in the nest will begin expanding the tunnel structure the following year. Tunnel structures can become quite complex and do considerable structural damage. This damage can be extremely significant as a single house can theoretically host dozens of nests. It is not uncommon to find nine or ten carpenter bee holes on a single side of a home.

The best preventative against carpenter bee infestations is simply to paint all exterior wood. If your wood exterior is already infested, however, a more laborious process is involved. Carpenter bee treatment requires that each individual hole be treated with insecticidal dust capable of coating the walls of the tunnel. Carpenter bee holes sometimes need to be treated numerous times over a 1-2 week period. Only after each hole has been thoroughly treated with insecticidal dust is it safe to fill in the holes. Holes should be filled in with pieces of dowel rod coated in wood glue. After treating existing holes, the surface should be painted to discourage further drilling, all though there are insecticide sprays that can be applied to untreated wood surfaces that will deter carpenter bees, though these need to be repeated usually twice per year at least.

It is important that you do not try to plug carpenter bee holes before applying insecticide, as they are skilled diggers and this will only encourage them to dig out a new entry point.

One experience from one of our technicians: Carpenter bee numbers will only increase if they are not treated. Our technicians serviced a home in Pinckney a few years back where an owner had allowed a carpenter bee problem to go untreated for several years. The population had exploded; our technicians estimated no less than 1,800 holes on one single side of a cedar garage.

Don’t let this become the story with your home! Call Creature Control today if you think you are having issues with carpenter bees.