Carpenter Bees (Xylocopa spp.) are solitary insects considered pests because the female excavates tunnels in wood to create galleries for laying eggs and rearing young. The damage begins with a perfectly circular entry hole, approximately half an inch in diameter, which then turns at a right angle to follow the wood grain, creating extensive internal galleries. Over multiple seasons, this activity can weaken structural timbers, fascia boards, or outdoor wooden furniture, leading to recurring property damage.
Identifying the Wood-Boring Pest
Accurate identification is the first step, as Carpenter Bees are often mistaken for their beneficial relatives, the Bumblebees. The clearest visual difference is the abdomen. A Carpenter Bee has a large, shiny, black, and mostly hairless abdomen, often described as metallic.
In contrast, a Bumblebee possesses a fuzzy abdomen covered in dense yellow and black hairs. Male Carpenter Bees are frequently seen hovering aggressively near the nest site, though they lack a stinger and are harmless.
Female bees leave a distinct pile of coarse, yellowish sawdust, known as frass, directly beneath the entry hole. This activity starts in the spring when adults emerge from overwintering tunnels to mate and begin boring new nests. They prefer unpainted or weathered softwoods like pine, cedar, or redwood, and tunnels can be reused and expanded annually.
Immediate Active Treatment Options
The most effective method for eliminating an active infestation involves applying an insecticidal dust directly into the tunnels. Dust formulations, such as those containing deltamethrin or carbaryl, are superior to liquid sprays for this application. The fine dust particles coat the inside of the gallery and cling to any bees, larvae, or pupae present.
The dust should be puffed into the half-inch entrance hole using a specialized hand duster. This application method ensures the insecticide reaches the deepest parts of the tunnel network. When an adult bee enters or exits the treated tunnel, it contacts the dust and carries it further into the nest, ensuring the death of the bee and any developing offspring.
Dusting is most effective in the late spring or early summer after the female has finished laying eggs but before the new adults emerge later in the year. For individual, flying bees, a contact aerosol spray can provide a quick kill, but this will not eliminate the existing nest galleries or developing larvae.
Sealing Damage and Preventing Reinfestation
Killing the bees is only the first step; the tunnels must be properly sealed and the wood protected to prevent reinfestation. Wait at least 24 to 48 hours after applying the insecticidal dust to ensure all adult bees are dead or fully exposed to the treatment. Sealing the hole too quickly can trap live bees, causing them to bore a new exit hole and extending the original damage.
The best materials for repair are wooden dowels that match the size of the hole, or a firm wood putty or filler. Avoid using soft materials like caulk or expanding foam, as these can be easily chewed through and may interfere with the dust’s long-term effect on emerging larvae. Once the tunnels are plugged and the filler has cured, the area should be sanded smooth.
The most reliable long-term prevention is to paint or varnish all exposed, bare wood surfaces. Carpenter Bees actively avoid wood that has been treated with a protective coating. Supplementary methods, such as commercial bee traps placed near the affected area, can also help reduce the local population of adults looking for new nest sites.