Carpenter bees (Xylocopa species) are large, solitary insects known for boring into wood to create nests. They are often mistaken for bumblebees due to their similar size and yellow and black coloring, but carpenter bees are easily distinguished by their shiny, relatively hairless black abdomen. Unlike social bees that live in large colonies, carpenter bees work alone or in small groups to excavate galleries in wooden structures. This wood-boring behavior can cause structural damage to homes and property over time. Understanding the timeline of their presence is the first step in addressing a potential infestation.
The Annual Cycle of Visible Activity
Carpenter bees are present throughout the year, but their visible activity outside of tunnels is concentrated into two seasonal windows. The first and most noticeable period occurs in the spring, typically beginning around March or April as temperatures rise. Adults emerge from hibernation sites to mate and begin nesting, representing the peak of their activity. Females actively search for new wood or refurbish existing tunnels, while males aggressively fly near nest entrances, guarding the area, though they are harmless as they lack a stinger. This intense period of drilling, mating, and egg-laying lasts until early summer, around June.
A second, less intense period occurs in late summer and early fall, usually in August or September. This marks the emergence of the new generation of adults from the wooden galleries. These young adults feed briefly on nectar and pollen to build energy reserves before seeking shelter. Once the weather cools, they return to the tunnels to overwinter until the following spring, when the cycle begins again.
Lifespan and Developmental Timeline
The lifespan of an individual adult carpenter bee is approximately one year, which includes a short period of activity followed by a long overwintering phase. Females begin laying eggs in late spring or early summer, placing each egg in a separate chamber within the tunnel. Each chamber is provisioned with a ball of pollen and nectar, and then sealed with a plug made of chewed wood fibers.
The immature stages—egg, larva, and pupa—undergo a relatively quick development period within these sealed cells. The total time from egg to adult emergence typically takes about seven weeks. Larvae feed on the stored pollen and nectar until they transform into fully formed adults. The new adults emerge during the late summer and early fall months. They forage briefly to build up energy before retreating back into the tunnels to hibernate until the following spring.
Duration of Nesting and Tunnel Damage
The physical damage caused by carpenter bees is a matter of both immediate excavation and long-term persistence. A female bee uses her mandibles to bore a nearly perfect, half-inch diameter entrance hole perpendicular to the wood grain. Once inside about an inch, she turns and begins excavating a tunnel that runs parallel to the wood grain.
A female can excavate a new gallery at a rate of approximately one inch every six days. Given that a single tunnel can extend from six inches up to four feet in length, the process of creating a full nest can take several weeks. Since females prefer to reuse and expand existing tunnels rather than bore entirely new ones, the damage to a specific wooden element is cumulative over time.
The tunnels themselves are a permanent fixture unless physically repaired. Subsequent generations of bees will return to the same location year after year, expanding the existing galleries and creating new side tunnels. This means that the structural consequence of their presence “stays around” indefinitely, as the weakened wood remains vulnerable to further infestation and expansion of the internal network of nesting chambers.