Carpenter bees (Xylocopa) do not burrow in the ground to create their nests. These large, often black or metallic-colored insects are wood-nesting species. Confusion often arises because they resemble the common bumblebee, which frequently establishes colonies in or near the ground. Carpenter bees are widespread and excavate tunnels in wooden structures to rear their young. Their nesting behavior focuses entirely on wood as their preferred habitat.
The Preferred Habitat: Wood Excavation
Female carpenter bees begin nesting by boring into wood, preferring soft, weathered, or unpainted lumber such as cedar, pine, or redwood. The entrance hole is perfectly circular, about one-half inch in diameter, often looking like it was created with a drill bit. After penetrating the wood, the female makes a sharp, ninety-degree turn and excavates a tunnel, known as a gallery, that runs parallel to the wood grain.
These galleries can extend for several inches, sometimes up to a few feet, especially if old tunnels are reused and expanded. The female partitions the gallery into a series of small, individual chambers, creating about five to six cells per tunnel. Each cell is provisioned with a mixture of pollen and nectar, called “bee bread,” upon which a single egg is laid. The cell is sealed with chewed wood pulp, providing the larvae a protected food source until they emerge as adults.
Common Confusion: Bees That Do Burrow in the Ground
The belief that carpenter bees burrow in the ground stems from their physical resemblance to other species that exhibit this behavior. Bumblebees (Bombus species) are similar in size and often have yellow and black markings. These social insects commonly nest close to or in the ground. A bumblebee queen often establishes a colony in an existing subterranean cavity, such as an abandoned rodent burrow, or under grass or leaves.
A large percentage of all bee species, estimated to be around 70%, are solitary and nest in the ground, including mining or digger bees. These solitary bees excavate small tunnels in the soil, often creating tiny mounds of dirt that resemble miniature volcanoes. Each female works independently, constructing and provisioning her own nest chamber. Neither social bumblebees nor solitary ground-nesting bees pose a threat to wooden structures, which is the primary concern associated with carpenter bees.
Visual Identification of Carpenter Bee Activity
Identifying a carpenter bee and its activity is straightforward by observing physical characteristics and external signs of damage. The easiest way to distinguish a carpenter bee from a bumblebee is by examining the abdomen: a carpenter bee has a smooth, shiny, mostly hairless black abdomen, while a bumblebee is fuzzy all over. The male carpenter bee, which cannot sting, is often observed aggressively patrolling and hovering near the nest entrance, displaying territorial behavior.
The clearest evidence of their presence is the debris left behind when excavating wood. Fresh, coarse sawdust, known as frass, is often found piled directly below the entry hole. Additionally, yellow or brownish-yellow staining, which is the bee’s fecal matter, can accumulate near the entrance. The sound of a rasping or drilling noise emanating from the wood during warmer months is another definitive sign of active tunneling.