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May 19, 2015

Carpenter Bees are Back!

Tim Gibb, Insect Diagnostician, Department of Entomology, Purdue University

Carpenter bees are back at it again and the result is a few holes in wood and lot of people calling for diagnosis and advice.

A carpenter bee approximates the bumblebee in shape and size but is nearly all black and has a much more naked (hairless) abdomen.

If descriptions include, a bee working around a nearly perfectly round, 1/2 inch diameter hole in wood, you can be sure that this is a carpenter bee.

The hole actually 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.

Each of these cells contains one bee larva. After the cells are completed, the female seals the tunnel and soon dies. Larvae inside the cells mature by late August and new adults emerge by early September. These adults forage for nectar but eventually reenter the tunnel (or a nearby one), clean it, and then overwinter in it. The cycle starts anew the following spring.

Note that carpenter bees may refurbish an existing tunnel instead of boring a new one, that an infestation may persist for several years or more, and that new tunnels are often constructed near old ones.

The carpenter bee actually causes little serious damage, although continuous tunneling over many years may eventually 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 can sting if handled.

On occasion woodpeckers are attracted to the tunnel looking for a free meal. Their damage to the wood in trying to get at the bee larvae inside becomes much more serious than the hole created by the bee.

Control can be safely and effectively accomplished by dusting into the tunnels with 5% Sevin, leaving them open for a few days and then plugging the opening with a dowel or wood putty to discourage future use.

E-252: Carpenter Bees (pdf file)

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