Carpenter bees are large insects known for their ability to bore into wood, a habit that makes the duration of their annual activity a concern for property owners. These solitary bees do not consume wood, but they excavate smooth, half-inch-wide tunnels to create nests for their offspring. Since the bees often reuse and expand existing galleries year after year, understanding their yearly timeline is important for managing potential structural damage. The length of their active season varies significantly based on geographic location and local climate conditions.
The Timing of Spring Emergence
The start of the carpenter bee active season is closely tied to rising temperatures following the winter months. Adult bees that survived the cold period in a dormant state emerge from their overwintering tunnels once the weather warms sufficiently. This emergence is typically triggered when ambient temperatures consistently reach around 70°F.
Geographical location dictates the precise timing of this initial activity, which can vary by months across the country. In the southernmost United States, emergence can occur as early as late February or early March, leading to a much longer season. Conversely, in northern states, the start of the active period may be delayed until late April or even May. Following emergence, the adults feed, mate, and the females begin searching for suitable unpainted or weathered wood surfaces to start nesting.
Peak Activity and Reproductive Duration
The most damaging phase of the carpenter bee life cycle begins immediately after mating, when the female starts constructing or expanding a nest gallery. A female bee uses her mandibles to chew through wood, a labor-intensive process that can take her about six days to drill just one inch of tunnel. She may bore a tunnel that extends a foot or more into a wooden structure.
Once the main gallery is complete, the female divides it into a series of individual cells, laying a single egg and provisioning it with a mixture of pollen and nectar. This egg-laying phase generally occurs from mid-to-late spring through early summer. The entire developmental process, from egg to adult bee, takes approximately seven weeks, though this timeline can be influenced by temperature.
The eggs hatch into larvae, which feed on the pollen provision for several weeks before entering the pupal stage, all within the protective wooden cell. The new generation of adult carpenter bees typically develops and chews its way out of the tunnel in late summer, usually around August or September. These newly emerged adults spend a few weeks feeding on nectar and pollen, representing a second peak in activity before they seek shelter for the winter.
Overwintering and the Inactive Period
The inactive period for carpenter bees begins as daylight hours shorten and outdoor temperatures consistently drop in the fall. The newly emerged adults from the late-summer generation prepare for a period of dormancy known as diapause. They retreat into the existing wooden tunnels where they were born, or into other safe wooden galleries.
During this time, the older generation of parent bees that constructed the nests often die inside the tunnels after completing their reproductive cycle. The young adults remain within the wooden structures in a hibernation-like state, often grouping together in a single chamber, facing away from the entrance. This dormant phase typically lasts from late fall through the cooler months of early spring, meaning the bees are physically inactive and cause no damage for several months of the year.