Most types of North American bees are purely beneficial species that are essential for pollinating plants, including the flowers and trees in our gardens and the agricultural crops that feed us. In 2006, a catastrophic decline in important bee species was first noticed, which has been attributed to several environmental problems, and the reduction continues to persist in 2020. Pesticides, loss of habitat, climate change, and disease have devastated bee populations in a phenomenon labeled "colony collapse disorder," in which the majority of worker bees in an established colony die.
Not all bee species are beneficial, however. Carpenter bees (Xylocpa spp.) are quite different from the garden bumblebees (Bombus spp.) and common honeybees (Apis spp.) that are so important for plant pollination. Carpenter bees are so-named for their nesting behavior, which involves burrowing into dead wood material, which can include the structural wood in homes and other buildings.
Carpenter bees are a type of bee that should be combated when you find them, but you can't do this unless you first identify them. How do you know if the bee you see is a beneficial bumblebee or honey bee, or if it's a damaging carpenter bee?
Each type of bee has distinguishing characteristics that will become clear if you look closely:
- Carpenter bees are 1/2 to 1 inch long, similar in size to bumblebees.
- Honey bees are usually around 3/4 inch long, in the middle of the range of carpenter bees.
However, size alone is not enough to identify what type of bee you're looking at.
- Carpenter bees can be black, green, or purplish.
- Bumblebees always have fuzzy bands of yellow and black.
- Honeybees have heads and legs that are black, with a central body (thorax) that is pale yellowish. The rear portion of the body (abdomen) alternates with dark and orange-yellowish bands.
- Carpenter bees have shiny black, hairless abdomens and the body segments have clear separations.
- Bumblebees are fluffy and fuzzy, and the body parts are not easily distinguished.
- Honeybees have furry thoraxes, with smooth shiny abdomens.
- Carpenter bees nest in the dead softwood of trees, homes, and other structures. They will carve out their nesting cavities.
- Bumblebees nest underground, from which they fly forth to flowers to gather pollen. They are rarely found in structures.
- Honeybees nest in hives with visible combs filled with small cells. Usually, these nests will be commercial hive boxes, although honeybees may nest in hollowed trees or other structures.
- Carpenter bees are unlikely to sting. The males are unable to sting at all, while the females are capable but rarely do so unless threatened.
- Bumblebees are generally intent on nectar gathering and rarely sting unless physically touched. They may also sting if the nest is disturbed, such as if you accidentally step or sit on it.
- Honeybees will sting if the hive is threatened or if they are physically touched. They rarely attack aggressively.
Carpenter Bee Damage
To create their nests, carpenter bees bore round holes into softwood, which they then build out with expanding tunnels and galleries, or “brood chambers.” Carpenter bees prefer softwoods, such as cedar, redwood, and soft pine that is at least 2 inches thick.
Initial damage is slight, but as the bees continue to build out their tunnels and chambers to raise successive generations, the structure of the wood can be damaged and weakened by the internal hollowing.
Carpenter Bee Nesting Behavior
In the spring, the carpenter bees mate, build or expand their nests, and lay their eggs.
For new nests, the carpenter bees first bore a round hole into softwood. For large species, the hole is about 1/2 inch in diameter; it is much smaller for smaller species. Once the hole is about an inch deep, the bee then turns its boring to follow the grain of the wood and create a tunnel, initially about 6 to 8 inches in length. Along the tunnel, the bees construct many individual brood chambers. Into each chamber is placed a ball of food made of pollen and nectar. Then an egg is laid in the chamber and it is sealed shut.
When the egg hatches, the larva feeds on the pollen/nectar mix and then emerges as an adult. This development takes place over about one month, on average, but can be longer or shorter depending on geography and temperature. The bees can produce up to three generations during summer, with each female depositing six to eight eggs in each brood.
The colony will overwinter in the wood, then mate and begin again the next spring, continuing to build out the tunnel and add breeding chambers as the population grows.
Signs of Infestation
The following are signs of carpenter bee infestation in wood:
- Like carpenter ants, carpenter bees do not eat the wood as termites do, but rather they excavate the tunnels, depositing the wood shavings outside the nest. Piles of residual wood and defecation outside the tunnel openings provide evidence of carpenter bees.
- Male carpenter bees will flit around the opening of the nest, guarding it against other flying insects and predators. Thus, if numerous bees are seen around your home’s eaves, doors, windowsills, decks, shingles, etc. where no hive is visible, they are likely carpenter bees.
- Carpenter bees will be seen going in and out of holes in wood from early spring through late summer in colder climates. They appear to vanish when the weather turns cold, as they overwinter in nests deep within the wood. They mate in spring, then emerge again to gather food in late spring and summer. In warm, southern areas, you may see the carpenter bees year-round.
Source: Penn State University Entomology