The species of most importance are about 1-inch long and have a robust, bee-like shape.
Like bumblebees, carpenter bees are black with some yellow. One carpenter bee species in the southwest, the
valley carpenter bee, has a metallic-black colored female and a tan colored male.
Carpenter bees chew out tunnels in wood in which to lay their eggs and provide a protected site for their
larvae to develop. The female bee selects a suitable log or piece of wood and chews a round, 1/2-inch diameter
tunnel into the wood. About one-inch deep, she turns at a right angle and chews a tunnel (nest gallery) about
12 inches in length. The bits of wood she chews off are deposited outside the nest and end up on the ground
below. These bits of wood, called frass, often are streaked yellow from pollen on the female s legs. An egg
will be deposited at the end of the nest gallery; the female will then pack the gallery about an inch deep with
pollen. This process is repeated until the entire gallery has been filled. The male carpenter bee guards the
outside of the nest and tries to chase away potential predators. He does not have a stinger, but still causes
concern with his aggressive buzzing if people venture near the nest site.
Carpenter bees are solitary insects that differ from other bees as they do not form colonies. Adults emerge
in spring to mate. Carpenter bees are so named because they nest in excavated galleries in wood; however, they
do not eat it, preferring to feed on pollen and nectar. They are actually important pollinators of flowers and
trees. They are generally cause cosmetic rather than structural harm to wood, but numerous generations can
cause considerable damage to existing galleries over time.
Using her strong jaws, the female carpenter bee will bore a clean cut, round entrance hole on the lateral
surface of wood that will evolve into a sort of gallery over time. It is a time and energy consuming process
and they prefer to enlarge an old nest rather than excavate a new one. The female will work into wood
perpendicular to the grain for 1-2 inches and then make a ninety-degree turn and excavate along the wood grain
for 4-6 inches to create a gallery or tunnel.
Carpenter bees are solitary insects that differ from other bees as they do not form colonies. The male does not
live long, so after mating in the spring, the female alone forms 6-10 “brood cells” inside. They consist of a
formed ball of pollen and regurgitated pollen at the far end of the gallery. She lays an egg on this mass,
which is walled off with a plug of chewed wood pulp, and dies soon after this labor. The larvae feed on the
mass until adulthood, which usually takes around seven weeks.
The new adults stay in the gallery for several weeks and then chew through the cell walls and venture out in
late August. They collect and store more pollen and travel back and stay in the gallery through winter,
emerging the following spring to repeat the cycle. Male Carpenter bees are considered a nuisance pest but are
harmless to humans as they lack a stinger. Females do have a stinger, but are typically docile and tend to
sting only when handled.
In nature, logs and dead trees and limbs are the targets for carpenter bees as nest sites. On homes, bare
wood decks, fences, and window sills is usually attacked. Painted wood, however, is subject to attack although
bare wood is preferred.
Carpenter bees nest in a wide range of softwoods and hardwoods, particularly if
it they are weathered. It is easier for them to tunnel through woods that are soft and have a straight grain.
They typically prefer softwoods such as pine, fir, cedar, cypress, oak, and redwood.
Carpenter bees also attack structural woods and other wood products, such as fence posts, utility poles,
arbors, firewood, and wooden lawn furniture. In buildings, they nest in bare wood near roof eaves and gables,
fascia boards, porch ceilings, decks, railings, siding, shingles, shutters, and other weathered wood. They tend
to avoid wood that is well-painted or covered with bark.
Carpenter bees usually do not make their entrance hole in an exposed area. The inner lip of fascia boards is a
common site of attack, as well as nail holes, exposed saw cuts, or other weakened areas.
Though carpenter bees seldom cause significant structural harm, their repeated colonization of the same wood
and the use of the same colony over many generations can eventually cause considerable wood damage.
Carpenter bees sometimes build new tunnels near old ones, which they continuously labor to enlarge and
refurbish. A gallery can extend for 10 feet or more over time. Replacement is necessary when the strength of
structural beams, posts, poles, and other wood products is reduced from bee damage.
They also leave unsightly damage by depositing yellowish to brownish streaks of excrement and pollen on
surfaces below entry holes.
keep all exposed wood surfaces well painted with polyurethane or oil-base paint
to discourage Carpenter bees from excavating since they can easily attack exposed wood. Seal existing holes
with caulking, wood putty, or a wooden dowel affixed with wood glue. If possible, fill the entire gallery with
sealant. Carpenter bees will not chew their way out of a sealed gallery due to behavioral constraints.
In new nests, larvae and pupae can be killed by inserting a long wire into the entrance hole and probing into
the gallery as far as possible. Wood stains will not prevent damage, so consider using aluminum, asphalt, vinyl
siding and similar non-wood materials that Carpenter bees avoid.
Painting bare wood that is being attacked by carpenter bees can deter some bees; however, it does not offer
the best solution.
- If the wood targeted by bees is treated with a residual pest control product, carpenter bees may be
repelled or killed by the treatment.
- Once holes have been started, the nest galleries may be treated.
- The holes can be plugged several weeks later when it is positive that the bees have been killed.