Every spring we get lots of calls about carpenter bees drilling into
logs, fascia boards, eaves, decks and other unpainted wood surfaces.
Carpenter bees are big black solitary bees that look similar to bumble bees
but have bare, shiny backs whereas a bumble bee’s back is hairy. Unlike
honey bees that reproduce in hives, carpenter bees drill into wood to lay
their eggs. Their holes are perfectly round and about 1/4-inch in diameter.
Although carpenter bees prefer softwoods such as cedar, redwood, or
cypress, they happily attack pine and most other species of wood. Even
pressure treated wood is not immune from carpenter bee attack. As the bee
drills into the wood, coarse sawdust may be seen coming out of the hole and
piling up beneath. Since it only takes a couple of hours for a carpenter bee
to drill a hole a few inches deep, lots of holes can appear over a fairly
short period of time.
Most carpenter bee activity occurs in early spring when male and female
bees emerge after spending the winter in old nest tunnels. Once they have
paired and mated the female bee drills into a suitable site while the male
stays nearby to ward off intruders. Male carpenter bees often frighten
people with their aggressive behavior, but since they have no stinger they
are essentially harmless. Females have a stinger but only use it if
molested.
Once the initial hole is drilled through the surface, the bee will make a
turn and excavate a tunnel along the grain of the wood. This tunnel, which
may run for several inches, becomes the cavity where the female deposits her
eggs. Several eggs are laid in individual chambers separated by plugs of
pollen on which the larvae feed until they emerge as adults during the
summer months. In addition to making new holes, carpenter bees also enlarge
old tunnels and, if left unattended for several years, serious damage to
wood may result.
In late fall, activity may again be seen as both male and female
carpenter bees clean out old nest cavities where they over-winter. Since
carpenter bees tend to migrate back to the same area from which they
emerged, it is important to implement some control measures in order to
prevent logs and wood members from becoming riddled by these bees.
Prevention
Although carpenter bees prefer bare wood, they will attack wood that is
stained. Painted wood surfaces, on the other hand, are rarely attacked since
the bees must see or feel the grain of the wood in order to recognize it as
wood.
Carpenter bees may be deterred from chewing into wood by spraying
pesticides such as Bayer Advanced Home/Lawn & Garden Insect Killer,
Spectracide Bug Stop and Ortho Home Defense System onto wood surfaces.
However, the effectiveness of these applications is only about 7 to 14 days,
so the treatment will have to be repeated often. These products should only
be used during periods of peak activity in the spring and perhaps again in
late fall. Be sure to follow label directions and read and understand any
precautions that must be taken when using these products.
One of the most effective measures for preventing extensive carpenter bee
damage is to fill old or empty holes with Energy Seal. Carpenter bees are
attracted to existing holes. Be sure to treat the hole before you fill it
since live adult bees will drill right through the caulk on their way out.
Treating Carpenter Bee Holes
The way to treat an existing hole and tunnel depends on the time of year and
if bees are present at the time of treatment. If the female is drilling away
when you find a hole (you can see sawdust coming out or hear her working
inside) spray a contact pesticide like wasp and hornet spray into the hole.
She will quickly back out and die. Immediately fill the hole with Energy
Seal.
If the hole is empty or you’re not sure if there is a bee in the
tunnel, insert a pesticide dust such as Armor-Guard powder into the
hole and leave it open for a few days so the bee contacts and distributes
the pesticide throughout the tunnels. Then fill the hole with Energy Seal.
If you find carpenter bee holes in the summer months, it’s difficult to
tell if there are bee larvae developing in the tunnels. The best thing to do
is to run a length of flexible wire into the tunnels in order to break
through the pollen plugs separating the chambers. Then spray an aerosol
pesticide or insert some Armor-Guard powder into the hole and seal it up.
The same thing should be done on holes found in the fall or winter to
kill any bees that may be overwintering. The key to carpenter bee control is
not so much what you use as knowing how and when to use it.
