From personal observation and talking with others, this seems to have been a good year for carpenter bees, as there have been plenty of them. Most of the questions I’ve been asked about them is how to get rid of them.
The eastern carpenter bee (Xylocopa virginica) look very much like a bumblebee, being around an inch long, kind of chubby, with black and yellow coloration. You can tell them apart by looking at the abdomen, which on a carpenter bee will be shiny, while that of the bumblebee is dull and covered with dense hair. You’ll most likely notice them in the spring and early summer when they are buzzing around looking for nesting sites, which unfortunately may be your house or outbuilding. You may also see clues of their wood tunneling activity, such as sawdust on the floor, and maybe some yellowish to brownish bee poop. The males are territorial and may swoop at you if you get near a nest, but they lack a stinger and are harmless. The female has a stinger, but tend to be docile and will only sting if caught or directly provoked.
The life of a carpenter bee goes something like this: Adults overwinter within old nest tunnels, emerging in April or May. After mating, the female excavates tunnels by vibrating her body and using her mandibles like a rasp to carve out a perfectly round half inch wide hole. It’s a noisy process and you’ll likely hear her buzzing away inside the wood. She first makes an entrance tunnel, and then builds other brood tunnels off of it. The whole purpose of the tunneling is to create a nursery to rear a new generation of bees. The female will create a row of cells, and into each depositing an egg and a blob of nectar and pollen. Each cell is sealed with a partition made of sawdust. The larvae hatch in mid-summer, feed and grow on the stockpiled food, and then emerge as adults in late summer.
The tunneling activity is what gets people’s attention, as nobody wants their buildings chewed on. Bare, unpainted or weathered softwoods are preferred, especially redwood, cedar, cypress, pine, and yellow poplar. Pressure treated lumber is supposedly less preferred, but I’ve seen them use it. Preferred places to tunnel include roof eaves, window trim, facia boards, siding, decks, and even outdoor furniture. The best way to deter the bees is to paint all exposed wood surfaces if that’s feasible, the thicker the better. Wood stains are less reliable than painting, but are better than nothing.
If you don’t want to use pesticides, you can try just plugging up the entrance hole with wood putty or caulking. Surprisingly, the female will not try to burrow her way out. If you want to go the insecticide route, liquid sprays can be applied to wood surfaces to deter females from starting tunnels (always follow label directions). These will have to be reapplied every one or two weeks. If tunnels are already present, they can be treated by squirting a little insecticidal dust into the hole. An aerosol spray labeled for wasps and bees can also be shot into the entrance hole, but be careful not to get any on you or especially in your eyes. Leave the hole open a few days to allow the bees to contact and hopefully spread the insecticide inside the tunnels. Then plug the entrance with some suitable material to protect against future use by the female, who often reuse old tunnels.