Eastern carpenter bees (Xylocopa virginica) are large, robust insects often seen hovering near wooden structures. Their presence is announced by perfectly circular holes drilled into eaves, fascia boards, or deck railings. This activity leads many to conclude the bees are consuming the wood, similar to termites. However, the wood is not a source of nutrition but a necessity for the survival of the next generation.
The Core Misconception: Do They Really Eat Wood?
The assumption that carpenter bees consume wood is a common misunderstanding stemming from the visible damage they cause. Unlike termites, which digest wood cellulose for sustenance, the carpenter bee does not eat wood at all. The adult bee’s diet consists exclusively of pollen and nectar gathered from flowering plants, providing the energy required for flight and reproduction.
When a female bee excavates a tunnel, the chewed wood material is not swallowed or digested. This material, which resembles coarse sawdust, is simply discarded outside the entrance hole. This waste material is called frass, and its presence beneath a bored hole indicates a carpenter bee is at work. Some wood particles are later repurposed by the female to construct internal partitions within the nest.
The True Purpose: Creating Nests and Larval Chambers
A female carpenter bee bores into wood solely for shelter and reproduction. These bees are solitary and do not form large colonies or hives; the tunnels function as a nursery for their young. In the spring, after mating, the female seeks a suitable wooden site to excavate a gallery for her eggs.
The female creates a series of individual chambers, or brood cells, along the length of the tunnel, which may extend up to a foot. Before laying an egg, she provisions each cell with a dense mixture of collected pollen and nectar, commonly called “bee bread.” This bee bread serves as the only food source for the developing larva once the egg hatches.
After placing a single egg on the food mass, the female seals the chamber with a partition made from chewed wood pulp mixed with her saliva. She repeats this process, creating a linear series of six to eight cells, each containing an egg and a provision of food. The larvae develop over the summer, feeding on the bee bread, and eventually emerge as new adults in the late summer or fall, ready to overwinter in the same tunnels.
The Mechanics of Boring and Preferred Wood
The physical act of wood boring is accomplished using the female’s powerful mandibles, which are strong, sharp jaws designed for chewing and scraping wood fibers. The process begins with the bee creating a perfectly circular entrance hole, typically one-half inch in diameter, drilled across the wood grain. Once inside, the bee turns at a right angle and begins tunneling parallel to the grain, which is the path of least resistance.
Carpenter bees are selective in the wood they target for excavation, preferring softwoods such as pine, cedar, redwood, and cypress. Wood that is unfinished, unpainted, or weathered is significantly easier for the bee to grip and penetrate, making these surfaces the most susceptible to attack. Painted or pressure-treated lumber is far less likely to be chosen for a new nest, as the surface coating creates a barrier that complicates the initial boring process.