From the Viette's Views Gardening Blog
The eastern carpenter bee, Xylocopa virginica, is a large bee that, at a quick glance, looks very much like a bumblebee. On closer inspection, though, you can see some distinct differences. The most obvious is the solid black, hairless abdomen that has no yellow coloration. Bumblebees have stripes or patches of yellow hair on the abdomen. The only yellow hairs on the eastern carpenter bee occur just behind the large head on the thorax.
The other main difference between carpenter bees and bumblebees is that bumblebees are social bees which nest underground. Carpenter bees are solitary bees and build their nests by “drilling” a tunnel into wood, creating a nest very similar to the nests created by the solitary ground bees.
Like the ground bees, it is the female carpenter bee that excavates the nest. She starts by drilling a perfectly round tunnel into bare wood perpendicular to the grain. Once the tunnel is about an inch long, she makes a right angle turn and continues her excavation with the grain of the wood. Unlike termites, carpenter bees do not eat wood, rather they “kick” it out of the tunnel leaving the telltale sawdust pile under the hole.
So much of the carpenter bee nesting behavior is similar to the Andrenid bees I wrote about last time. The female bee goes out and collects pollen and nectar, carries it to the nest, forms it into a ball and lays a single egg on it. She then uses some sawdust to partition off the compartment, creates another pollen/nectar ball, lays another egg, partitions that off, and so on until the tunnel is filled. She may create up to 8 or 10 separate compartments within the tunnel. When the eggs hatch, the larvae feed on the pollen ball, pupate, and eventually emerge as adults around August. These young adults feed on the nectar of late summer and fall flowering plants and then return to overwinter in the nest. They re-emerge in the spring, mate, and then the cycle begins again.
We caught this female carpenter bee in the process of excavating her nest. I could actually hear her rasping or chewing the wood as she was enlarging the tunnel – it was pretty interesting. We flushed her out by squirting a little water into the hole and out she came, a little sodden but otherwise unharmed.
Carpenter bees can be a nuisance at times but, like the solitary ground bees, they are important pollinators and should be tolerated if possible. These bees are generally not aggressive; the males do not have stingers and the females will only sting if they are really provoked.
In most cases, their tunneling simply causes cosmetic damage to the wood, however, since subsequent generations often reuse the same nest and may expand the excavation, structural damage can sometimes occur.
Carpenter bees tend to seek out unpainted wood for their nests and will target unpainted doors, windowsills, fascia boards, exposed rafters, roof eaves, deck railings, and sometimes wooden lawn furniture as in our case. Painting or varnishing exposed wood is one way to dissuade them from drilling into your wooden structures and most of the time, this is enough to keep them away.
If it’s too late for paint and they are building a nest in an area where they will cause problems, an insecticidal dust like Bonide Termite and Carpenter Ant Dust can be puffed into the hole according to the label directions. This will take care of the female bee and a reapplication in midsummer will take care of the emerging adults in August. In the fall, plug the hole with a wooden dowel or wood putty and paint the surface to keep bees from nesting there in the future.