When you see a small hole in wood with sawdust coming out of it a red flag probably goes up and you want get rid of whatever is making the hole. But stop. Chances are that you have a female carpenter bee a potential friend in the garden. Carpenter bees are significant pollinators and the damage they cause is usually cosmetic rather than structural.
Carpenter bees are about the size of a bumblebee, smaller or larger depending on the species. The two kinds of bees are also similar is coloration but the upper surface of a carpenter bee’s abdomen is bare and shiny black while the bumblebee has a hairy abdomen with some yellow markings. Some species of male carpenter bees have white or yellow faces and may have larger eyes than female carpenter bees. The males can be aggressive when defending their territory but since they have no stinger they are more of an annoyance than a danger. If a huge dive bomber bee with a loud buzz comes after you until you leave the area it is probably a male carpenter bee. Females, on the other hand, do have stingers but are generally not aggressive unless man handled.
Carpenter bees are not usually social insects and do not live in colonies. Solitary females usually create tunnels in wood to lay their eggs and prefer unpainted, untreated, softwood, especially pine, cedar, cypress and redwood. Siding, decks, window trim, eaves, and outdoor furniture all provide desirable nesting sites. The adults spend the winter in old nesting tunnels and emerge in the spring to mate, make new nesting tunnels or enlarge old ones, and lay their eggs. They leave a well-formed mass of pollen as food for each egg. Although carpenter bees are not considered social insects they may be gregarious and many females may form tunnels near each other. If the tunnels are made in an area year after year the damage can be considerable. Painting all exposed wood surfaces is a good way to discourage them since they like bare, weathered wood. In addition, fill all holes, especially the old tunnels of carpenter bees and paint over the repairs.
Why bother? Carpenter bees are good pollinators especially of tomatoes and open-faced flowers and they are good companions in the garden adding life to every area they frequent. With populations of honeybees declining we should try to accommodate the pollinators we still have.
Would you like to know more about bumblebees? See my post How and Why to Attract Bumblebees to the Garden.