Carpenter bees are their own specific category of bees, the genus Xylocopa, and they are not bumblebees, which have very different breeding and life cycles and social systems. Most species of carpenter bees have a glossy black abdomen and fuzzy thorax which may be honey coloured, black, or even bright electric blue, as in Xylocopa caerulea, which lives in southeast Asia. They are generally docile and non-aggressive, but the females are capable of delivering multiple stings, and they do not die when they sting, the way honeybees do.
Here I wish to address a single specific species within the Xylocopa genus of bees, the Eastern Carpenter Bee, Xylocopa virginica virginica, which will be the only wood bee species encountered by most people living in North America. This is the species with which I have the longest acquaintance.
Eastern carpenter bees, "wood bees" to locals, are a presocial bee species, unlike the eusocial European honeybee. This means that, instead of having a single fertile queen, a few dozen male drones, and thousands of sterile female workers, the wood bee society consists only of fertile females and males who spend most of their lifespan together, divide labour, and to some extent take care of their hatched young. They are a non-colonial bee species, but late in the season after the males have died, sister bees will sometimes form working pairs, taking turns tunneling their nests, harvesting pollen for food, and protecting the nest. The generations of hatching bees are somewhat staggered, so that there may sometimes be a few hibernatory adult females in the nest along with the hatching larva, when the hatching begins, and these last lingering adults will only just begin to die out when the next generation is emerging from the pupal stage. The number of generations per season or year is limited by the local climate, and areas with a temperate autumn and winter will have fewer wood bees overall than more tropical zones.
Wood bees are the largest true bee species, and very few other hymenopterans are much larger- mostly hornets and ants living in tropical rain forest regions. The largest wood bee I have personally seen was nearly 5 cm long, and I initially mistook the sound of his wings for a hummingbird, or a helicopter built for Borrowers. He hovered directly in front of my face, investigating me, and upon verifying that the large creature was not a rival male, he took off in pursuit of an acorn which had fallen from a nearby oak.
Wood bee males are immense fun: they are stingless, they are easily identifiable by the large white spot on their forehead (a spot which the black-faced, sting-carrying females lack), and they are curious and have very poor vision by bee standards. This means that they will approach and investigate anything which moves, scaring the wits out of people frightened by bees, or chasing tossed pebbles and acorns. Two wood bee males facing off against one another is amusing, since neither of them has any natural weapons. They are all bluff, diving at one another in pint-sized games of chicken. Eventually, one leaves on his own accord, with no apparent indication why. Sometimes, they make such a fuss that nearby birds notice them, and one or both ends up on the menu for a flycatcher, shrike, or bee-eater.
The females have stingers, but it takes some serious provocation to incite a sting. A female wood bee's entire focus is on hollowing a piece of dry wood for her eggs, and leaving enough stored food available for the young when they hatch. For most of the breeding season, male and female wood bees will pair off monogamously, and the male will occasionally bring back plant pollen and nectar for the female, when he is not preoccupied with rival males. Male wood bees are among the most important pollinators in the United States Midwest, because the timing of their emergence tends to be earlier than the emergence of honeybees, meaning that they are able to pollinate flowers sooner in the season. The female bees, however, present some problems for the plants which the males pollinate: especially very late in the season, after the more fragile males have died off, the female bees will sometimes "rob" nectar from flowers, carving neat holes into the side of the flower and stealing the nectar from below, without ever interacting at all with stamens or pistil. The bee gets her meal, but the flower does not get pollinated, and now it has no nectar left to attract other pollinators. Eastern carpenter bees are not as severe robbers of nectar as most carpenter bee species, but this could be attributed to the abundance of red clover plants in the midwest, which have especially abundant and available pollen for bumblebees and carpenter bees, whose probosces are longer than honeybees'.
Nectar robbing is not the only ecological problem offered by carpenter bees; the females also have pesky tendency to drill centimeter-wide, perfectly round holes into the undersides of wood beams on people's houses and barns. Every time a wood bee female creates a nesting tunnel, her daughters will continue using and deepening that tunnel for multiple generations, only changing locations when the current tunnel is too crowded by sisters from the same mother. The only way to completely eliminate this cycle, once it has begun, is to kill the entire local wood bee population at that nesting site, and this can only be guaranteed by coring out the nest tunnels and killing the larvae, or by completely replacing the damaged wood. There are alternatives, however, to using bee-killing chemicals which do not discriminate between bee species, and to replacing or carving into the wood on your front porch awning.
If you already have a wood bee problem at your house, your most immediately convenient option is to give them a better place to build their nests. Wood bees prefer unpainted, dry, unrotten wood over painted, wet, or rotten wood. They also prefer to avoid wood which has been treated for outdoor use. They create their tunnels almost exclusively on the undersides of wood, not on the flat sides which woodpeckers would be able to access easily. If you suspend a plank of wood horizontally someplace away from your house or other wooden structures, especially if the space is not directly exposed to rain and shear winds, then subsequent generations of wood bees will prioritize the plank over your house, which is inhabited and a high-traffic area which the bees would probably rather not inhabit anyway.
Another option is to make use of the abundant avian predators at your disposal: set out bird feeders to attract woodpeckers and other insect-eating birds. Bear in mind that woodpeckers will also do damage to wood, while seeking out their larval meal, and they won't restrict their pecking just to the nonliving wood which makes up your awning or the crossbeams in your barn; woodpeckers go for live trees, too, and they can do quite a bit of damage in large numbers. They are also damn noisy.
Iron Noder 2013, 13/30