Carpenter bees are solitary bees that get their common name from their habit of boring chambers in solid wood in order to create living quarters for their larvae. Softer woods such as redwood may be preferred, and the wood is not eaten, but instead is reduced to sawdust (“frass”) which is ejected from the tunnels. The female bee does the excavating, and several females may be working in the same section of wood and using the same entrance hole, but creating separate galleries. Males and females over-winter in old galleries and emerge in the spring to mate. They will both die before the end of the summer and it is their offspring which begin the next year’s activity. The galleries may be used repeatedly, with each new female lengthening the tunnel, which often can be over 10 feet in length. She creates an average of 6 or 7 cells, each separated by a plug, and places an egg and a food supply of pollen and nectar in each cell. Once this is completed she never returns to care for the larvae.
Surface coatings of paint or varnish are somewhat repellent, but not always. Injection of a residual dust insecticide into the gallery opening, followed by placement of a plug in the opening, will confine the bees to this treated area if done at night. Holes can then be permanently sealed. Where the bees are creating galleries over large areas of exterior surfaces, such as siding, some protection may be provided by spot treating the most susceptible areas with a microencapsulated insecticide. In general, though, these are important pollinators and if they are not attempting to nest within important wood members they should not be harmed.