Carpenter bees are large bees that are often mistaken for bumble bees. They come out in the spring after overwintering in small holes (often they revisit the same holes they made in the spring) and proceed to lay eggs. They will either lay their eggs in previously made holes or they will make new ones. This can lead to several large holes in decking, railings, and other exposed wooden surfaces that can be unsightly, though they rarely cause structural damage themselves.
One of the primary reasons to plug carpenter bee holes is that they can open the door for other types of damage. Once the eggs are laid in the galleries (the long tunnel proceeding from the hole the bees make) they hatch into larvae, which woodpeckers love to eat. They will peck out the tunnel that is hidden under a layer of wood in order to feed on them. This can leave large (up to 12 inches) lengths of exposed wood that is open to water damage, mold and fungus, or other types of structural issues.
Treatment of carpenter bees and their galleries becomes necessary to avoid this type of damage in the future. Unfortunately there are no preventative treatment methods that are available. Each carpenter bee and/or gallery has to be treated individually. With a large infestation this can mean several treatments over several days, and even then new carpenter bees can show up to take their place. This is why we do not offer a carpenter bee treatment service for it is best done by the homeowner. There are several ways of treating them but the most successful is to inject pesticide into the hole and then seal it in such a way that it cannot be used again through the use of wire mesh, wood filler, caulk, or other methods. That way, when the weather cools down, the bees will not be able to reuse those holes either for their winter rest or for more eggs in the following spring.
Carpenter bees are, themselves, largely harmless. The males do not have stingers, and the females will very rarely sting. They will become aggressive if they perceive a threat but unless physically threatened or harmed in some way, the females will not sting. The real threat to your home comes from their tunnels, or galleries, that can lead to other types of damage later on.