The sight of a large, buzzing bee near a wooden structure often leads to concern about structural damage. Two common, similarly-sized bees—the bumble bee and the carpenter bee—are often mistaken for one another. Only one of these insects is responsible for boring holes into decks, eaves, and fascia boards. Knowing the difference protects your property while preserving beneficial pollinators.
The Bumble Bee’s Nesting Habits
Bumble bees are not the source of structural damage to homes or sheds. They are social insects that establish colonies, but they rely entirely on pre-existing, sheltered spaces for nesting. Queens look for cavities that offer insulation and protection from the elements to start new colonies. Preferred nesting sites often include abandoned rodent burrows, dense clumps of grass, or small voids under landscaping features. They simply occupy these spaces and do not chew or excavate the surrounding material.
The Real Culprit: Wood-Boring Bees
The carpenter bee, belonging to the genus Xylocopa, is the source of wood damage. These solitary bees bore perfectly cylindrical holes into wood to create a nesting gallery for their young. The entrance holes are distinct, measuring about a half-inch in diameter.
Once a female drills about an inch deep, the tunnel turns abruptly at a right angle and runs parallel to the wood grain. These tunnels, called galleries, can extend six to twelve inches and are partitioned into small cells for individual eggs. Evidence of this activity includes coarse, sawdust-like droppings, known as frass, that accumulate directly beneath the entry hole. Successive generations may reuse and lengthen these galleries, potentially weakening thin or untreated wooden components.
Visual and Behavioral Distinctions
Differentiating between a bumble bee and a carpenter bee involves examining their bodies and observing their flight patterns. The most reliable visual characteristic is the abdomen. A bumble bee’s entire body is covered in dense, fuzzy hair, giving it a soft, robust appearance with yellow and black bands across its abdomen.
A carpenter bee, conversely, has a large, smooth, and shiny black abdomen that appears bare or polished. While its thorax is covered in hair, the lack of hair on the abdomen creates a stark contrast. In terms of behavior, male carpenter bees are known for their territorial hovering near nesting sites, darting at perceived threats. Bumble bees are generally more focused on foraging and fly in a more direct path between flowers and their nest.
Preventing and Addressing Wood Damage
Carpenter bees strongly prefer bare, unpainted, or weathered softwoods such as pine, cedar, or redwood for nesting. A primary preventative measure is to ensure all exposed wooden surfaces are covered with paint or a polyurethane finish, as this acts as a significant deterrent. Wood stains offer some protection but are not as effective as a durable paint coating.
If active nesting is found, treat the holes with an insecticidal dust, which is carried deep into the tunnels by the returning bees. Wait until late summer or early fall, after the bees are no longer active, to seal the holes with wood putty or a dowel. Sealing the holes too early can trap new adults inside, forcing them to chew new exit holes and causing further damage. For severe or widespread infestations, consulting a professional pest control service is recommended.