By Kathy Conner Cornell
VCE Southside Master Gardener
As I was working around one of my roses that is by an old shed, I was being swarmed by carpenter bees, Xylocopa virginica. It made me wonder if the carpenter bee serves any useful purpose besides being aggravating. Generally, the ones that fly around us are the males. You can tell this by the whitish square at the mouthpart. Males are very protective of the nest and that is why they buzz us. Males cannot sting. Females can but only sting if provoked. Females tend to not buzz around and you rarely know they are there. You’ll be happy to know the males die off shortly after mating.
A cutaway view of a carpenter bee nest. You will notice the individual brood cells.
Contrary to popular opinion, carpenter bees do not eat wood. They use their strong mandibles, jaws, to drill into wood to make a nest. This is where the problem to humans occurs. Sometimes our houses seem to make nice nest material especially if you have a cedar sided house like ours. The nest will go against the grain for an inch or two, then turn to go with the grain. In the spring, mating occurs. The female will make brood chambers in the excavated tunnel. Each chamber will contain “bee bread” which is a mixture of pollen and regurgitated nectar. The female will lay an egg in the chamber and then close it up with masticated wood.
To be fair to the carpenter bees, they will normally use dead trees for nesting sites or trees without bark. They prefer cypress, pines and junipers. But unpainted wood is fair game – old barns, picnic tables, wooden benches and maybe even corn hole boards. Apparently, the bees have no interest in painted or lacquered wood. That is supposed to be the remedy to keeping them from nesting in your siding, fascia or eaves.
The eggs hatch about a week to a week and a half after they are laid. They feed on the bee bread. Pupae remain in their cells for about 3 weeks. After pupation, the bees exit their brood chamber but remain in the tunnel. During this time, the adults may be fed by their mother or other brood mates. Thus, carpenter bees are considered primitively social. The new adults leave the nest in August. They feed and return to the nest to overwinter.
An unusual aspect of the carpenter bee life span, is that the females often live 2 years. Most female solitary bees die after they have laid eggs for next year’s brood. Carpenter females often share tunnels with their offspring and overwinter together. I could find no evidence that the female mate and goes through the process the second year. The nests are reused for many generations.
Carpenter bees are good pollinators of plants that need buzz pollination such as tomatoes and eggplant. Because of their size, many nectar sources are unavailable to them. They have a bad habit of using those mandibles to make a slit in the flower and suck out the nectar making it unappealing to the real pollinators of that flower. Carpenter bees are a food source for some birds, especially shrikes and woodpeckers, rodents and big headed ants. Fortunately, the big headed ant is not found in Virginia. I wouldn’t want to come across an insect that thinks fire ants are a tasty treat!
Bottom line, are carpenter bees a good bug or a bad bug? Yes. They are good because they pollinate crops. They are bad because they sometimes build nests in our siding. But it is comforting to know that even though the males are buzzing our heads and our pets, they will cause no harm. They also serve as a food source which is a good thing. For more information, see North Carolina State Extension’s publication entitled “Carpenter Bees”.
While we all are practicing ‘social distancing’ and Halifax County buildings are still closed to the public due to COVID-19, if you have gardening questions, you can reach an Extension Master Gardener or Extension staff member by sending an email to firstname.lastname@example.org. If you are unable to email, you can call and leave a message at the Halifax Extension Master Gardener Help Desk at (434) 830-3383. Be sure to give us your first and last name, telephone number and the nature of the call. The Help Desk phone is routinely checked. Someone will get back to you, although it may be from a different telephone number. Keep washing your hands, wear your mask, practice ‘social distancing’ and find comfort in the knowledge that those buzzing carpenter bees won’t hurt you