Carpenter bees are solitary insects that pose a threat to wooden structures by excavating nests to lay their eggs. Unlike termites, these bees do not consume wood. Instead, they drill perfectly circular, half-inch diameter holes into softwoods like pine, cedar, and redwood. This behavior, often signaled by coarse sawdust piles called frass beneath the entry point, can compromise the structural integrity of decks, eaves, and fascia boards over time.
Methods for Eliminating Active Bees
Targeting the active infestation requires applying an insecticide directly into the galleries the bees have bored. Insecticidal dusts are often the most effective method because they coat the interior of the tunnel. When the bees move through the gallery, the powder adheres to their bodies and is transferred throughout the nest, eventually killing adults and developing larvae.
Applying a specialized dust, such as one containing boric acid or deltamethrin, should be done with a hand duster directly into the entrance hole. It is important to treat every visible hole, as a single female can excavate a tunnel that extends up to ten feet along the wood grain. For the dust to work properly, the holes must not be sealed immediately; the bees need to remain active to track the toxicant deep into the egg chambers.
Treatment should occur in the spring or early summer when activity is highest. An alternative approach involves setting up specialized carpenter bee traps, which lure the bees into a central chamber using the appearance of a nesting site. These traps offer a chemical-free method of reducing the population and should be positioned near the infested areas for best results. For immediate contact kills, a short burst of an aerosol insecticide can be sprayed directly into the tunnel entrance.
Sealing and Repairing Damaged Wood
Once the active bees have been eliminated, the next step involves repairing the physical damage to prevent reinfestation. It is imperative to wait at least 48 to 72 hours after applying a dust treatment before sealing any entrance holes. Sealing too quickly will trap the bees inside, but they will simply chew a new exit hole, often creating more damage and bypassing the insecticide.
The primary method for permanent repair involves using wooden dowels. Choose a dowel that matches the half-inch diameter of the bee’s hole, coat it with exterior-grade wood glue, and tap it tightly into the opening. Using a hard material like a dowel is better than relying on caulk or wood putty alone, as soft sealants are easily chewed through by returning bees.
After the dowel is secured and cut flush with the wood surface, a thin layer of wood putty or filler can be applied over the repair for a smooth finish. Once the filler has dried, the repaired area should be sanded and primed in preparation for a protective coating.
Deterrents and Long-Term Prevention
Preventing future attacks hinges on making the wooden surfaces unattractive to the bees. Painting or applying a solid stain to all exposed wood is an effective long-term strategy. Carpenter bees strongly prefer bare, unfinished, or weathered wood, and a fresh coat of paint acts as a physical barrier that deters nesting activity.
For vulnerable areas like the underside of deck railings, eaves, and fascia boards, consider installing physical barriers such as fine wire mesh or specialized netting. This simple measure covers the wood surface while still allowing airflow, preventing the bees from reaching the wood to drill their initial entry hole. The mesh should be secured tightly around all edges to eliminate any gaps.
Another preventive measure involves using natural repellents around previously infested or vulnerable areas. Sprays made from almond oil or citrus oil, which contain compounds the bees dislike, can be applied to the wood surface. While these natural deterrents are effective, they require frequent reapplication, often every few days during the peak spring season, to maintain a consistent barrier. For new construction or replacement projects, choosing denser hardwoods or composite materials over softwoods eliminates the bee’s preferred nesting substrate, providing a permanent solution.