A sure sign of spring is the emergence of carpenter bees. Have you seen the perfectly circular small holes that these bees chew into wood? I mean honestly, I have trouble drawing a perfect circle freehand, much less chewing one!
Adult carpenter bees spend the winter hanging out in their nesting site, just waiting for the first signs of spring when they will emerge, find pollen for food, and mate. Nesting sites/holes are most often seen under the eaves of buildings, particularly on unpainted wood. Every spring, we have carpenter bees infesting the eaves of our barn.
People often confuse carpenter bees for bumble bees, but there are some distinct differences between these two types of bees, including nesting locations. Bumble bees live in a social hive whereas carpenter bees are solitary, and a carpenter bee has an abdomen that is shiny black, not hairy.
Carpenter bees are native pollinators, are not aggressive, and are only noticeable in late spring-early summer. They are mostly found around structures made of wood, or around facia trim, beams, etc.
Male carpenter bees often cause alarm when they dive-bomb and fly erratically around humans that approach nesting sites, but in actuality, these bees are bluffing as they lack a stinger and are harmless. They can be identified easily by the white spot on the front of their heads.
Only female bees have a stinger, which is a modified egg-laying device (ovipositor). Female carpenter bees are docile and are reported to sting only if handled, but a female carpenter bee can sting more than once.
Carpenter bees do not consume wood, but they do create their nesting sites in wood. They feed on pollen and nectar and are important plant pollinators. Their large size allows them to pollinate some flowers that are unsuitable to smaller bees.
Female carpenter bees use their strong jaws (mandibles) to chew a perfect circle entrance hole and make a small chamber that will become her home. The entrance is a little less than a half-inch wide, close to the same diameter as her body. These channels that she chews are perpendicular to the grain of the wood. Then they will turn about 90 degrees and excavate along the wood grain for 4 to 6 inches to create a gallery (tunnel). It takes approximately 6 days to bore one inch into the wood.
Female carpenter bees build several cells within each tunnel and each cell contains one egg and enough food for the larva that will hatch. The food, called bee bread, is a mixture of pollen and plant nectar. She places the food into the tunnel, lays a single egg on it, and builds a partition in the tunnel with cemented wood particles. Each tunnel contains 6 to 10 cells.
Control of carpenter bees may be desired if there is significant damage to wooden structures. But be aware, carpenter bees do not cause major damage like termites, and again, they are important native pollinators.
If control is desired, you can apply a registered insecticide into the entrance holes. Then the holes should be sealed thoroughly with wood putty or caulking compound. If possible, filling the entire tunnel system with a sealant can also be effective. All exposed wood surfaces should be painted or varnished and sealed. When managing carpenter bees, it may be helpful to treat and seal entrance holes during the early morning or late evening when bees are less active. Additional management options are offered by West Virginia University Extension.
References and Resources
By Ashley Bodkins, Senior Agent Associate and Master Gardener Coordinator, Garrett County, Maryland, and Christa K. Carignan, Coordinator, Home and Garden Information Center, University of Maryland Extension. See more posts by Ashley and Christa.