Carpenter bees (Xylocopinae subfamily) are considered to be important pollinators, especially of open-faced flowers, though they are also known to “rob” nectar by boring holes in the sides of flowers with deep corollas (thus not accomplishing pollination). The smaller species tunnel into pithy stems to build their nests. Other species bore holes in wood and can become pests in wood construction.
Carpenter bees are often mistaken for bumblebees. They are similar in size and coloring. The primary physical difference is on the abdomen. Carpenter bees have a shiny black abdomen. Bumblebees have a fuzzy abdomen with some yellow coloring.
Just like termites, carpenter bees are a problem for wood-framed homes. They make their nests by tunneling into wood, usually with an initial upward hole in any overhang. They then construct many horizontal tunnels. Because of their pollination skill, some people allow carpenter bees to stay around the home in the early spring, repairing the damage later. There are also programs for attracting carpenter bees to areas they are needed by supplying them with suitable nesting holes in blocks of wood.
Carpenter bees spend the winter as adults inside abandoned nests. Then, they emerge in the spring to mate and lay eggs. The female will usually bore longer tunnels in the nest for the eggs while the male collects pollen for larvae feed. Active nests in a home can cause considerable damage in just a few years.
Carpenter bee nests are rather easy to spot. They bore the opening hole directly up into the bottom of an overhang. The entrance hole is about 11 millimeters in diameter. Because the female continually bores longer tunnels, there is usually a collection of fresh sawdust below the hole. Also, the sound of a boring carpenter bee is very loud and can be heard easily. To deter carpenter bees from making nests in your home, you should keep all wood painted or stained. Paint is a better deterrent than stain, but it is important to avoid having bare wood available as it is very inviting to a bee looking for a place to start a new nest.
Male carpenter bees are curious and will investigate anyone, including humans that come near their nests. However, the males do not have stingers and cannot cause any real harm. The female carpenter bees are far more docile, but have the ability to cause a painful sting.
The best way to prevent carpenter bee infestations is to keep all wood surfaces treated with chemicals or coated with paint. The bees can quickly find a spot of bare wood, which they will carve into a home.
Once a carpenter bee nest has been located, it must be treated to kill the bees living inside of it. This may be done with any common bee/wasp spray. Because male bees protect the nests, they will likely swarm when you approach but will not sting. The female bees rarely leave the nest, but will when threatened and they can sting.
Once a nest has been killed, the entrance must be plugged. This may be done with glue or putty. Then, it should be treated or painted to keep the bees from coming back to the same location.
An alternative means of preventing infestations is to attract the bees to another location by propping a beam of attractive bare wood where you would prefer the bees to stay. The theory is that the bees will build their nests in the wood you supply for them and stay away from your house. However, it assumes that the population of bees will not increase, requiring your house for more nesting room.