Large Bees Active Around
Timothy J. Gibb, Insect Diagnostician,
Department of Entomology, Purdue University
Many complaints are currently
being forwarded to the laboratory concerning “large bumble
bee look-a-likes that bore into wooden structures.”
These are carpenter bees and
are very active during late April and throughout May in our area. They can be distinguished
from bumble bees by their nearly all black and a much more naked
(hairless) abdomen. Carpenter bees are often noticed working around
a nearly perfectly round entry hole in wood (pine, cedar, cypress)
that is about 1/2 inch in diameter. The hole goes straight into
the wood for about 1-2 inches, then makes a 90 degree turn and
runs with the wood grain for some 4-6 inches. The female bee fills
6-8 cells (separated from one another by partitions of wood pulp)
with pollen and nectar and an egg. She then seals the
tunnel and soon dies. Larvae inside the cells hatch, feed
on the store of pollen and mature by late August. New adults
emerge by early September. These adults forage for nectar but eventually
reenter the tunnel (or a nearby one), clean it, and then pass the
winter within it.
The cycle starts anew the following spring.
Note that carpenter bees may refurbish an existing tunnel instead
of boring a new one but new tunnels are often constructed near
old ones. This
means that that an infestation may persist for several years or
more in the same general location.
Individually, the carpenter bee actually causes little serious
damage, however, continuous tunneling in wood over several years
or by many bees may weaken the structure. Perhaps the biggest problem
is the annoyance and fear associated with the large carpenter bee.
Males patrol the area and often fly about the faces of people;
however, they cannot sting. The females do not defend their nest,
but will sting if mishandled.
Carpenter bees are less attracted to stained,
varnished painted or pressure treated wood, than they are to
seasoned bare wood. Control
of existing infestations can be safely and effectively accomplished
by dusting into the tunnels with 5% Sevin, leaving them open for
a day or so, then plugging the opening with a dowel or wood putty
to prevent future use. Pyrethroids applied to the outside
surface of the structure, where the bees may land, serves the same
purpose and may offer slightly longer residual control.
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Photo courtesy of John Obermeyer