Carpenter bees in spring flight

Chuck Adamson, Senior Information Specialist, Extension & Ag Information, University of Missouri

Carpenter bees may appear aggressive, setting up nests in eaves and near doorways and often hovering close to people’s heads as if ready to attack.

But they’re really the teddy bears of bees and nothing to fear, says Richard Houseman, University of Missouri Extension entomologist.

Because for all that hovering and buzzing, the males can’t sting and the females usually won’t.

“The male bees are just curious,” Houseman said. “They are always patrolling. If something comes in their area, they’re going to go check it out. If it’s another bee, they’ll chase it off. If it’s a human, they’ll probably just watch. The female has the power to give you a sting, but its temperament has not evolved to be aggressive.”

The carpenters, like pretty much all bees, are deemed beneficial insects because of their excellent work pollinating flower and vegetable gardens.

Carpenter bees can destroy wood though, making them an economic pest when they begin nesting in homes and other structures.

There are several carpenter bee species in the United States, but the one that is most common in Missouri is the species Xylocopa virginica.

It’s often mistaken for its close relative the bumble bee because of its size and shape. Carpenter bees have black, shiny, hairless abdomens.

Bumble bees’ abdomens are densely covered in black and yellow hairs.

Carpenter bees tend to hover around wood. Bumble bees, which are earth dwellers, fly slower and low to the ground.

The stinger-less carpenter males have white faces and are the ones most often seen hovering around wood decks and eaves.

The female carpenters have all black faces. During spring, they’re busy preparing egg cells inside tunnels.

Carpenter bees excavate almost perfectly round wood tunnels about a 1/2-inch in diameter. The tunnels typically run a few inches into the wood, then turn 90 degrees and run the length of the wood.

“The first year they’ll tunnel 10 to 15 inches. Each year after that, it will expand, up to 6 to 8 feet or more,” Houseman said. “The wood can be weakened after several years of nesting.”

Each female can build six to 10 single-egg cells. Larvae mature and emerge as fully developed bees in September. Then, they overwinter in the tunnels and reemerge the following spring. They die in July after mating and laying eggs. Each bee generation lives one year.

To eliminate nesting carpenter bees Houseman suggested getting a clean, dry plastic mustard bottle or similar squeeze-type dispenser. Fill it one-third full with insecticide dust. Houseman recommends Delta Dust.

Squirt the dust into the bee holes.

Apply dust at night and in cool weather when the bees are less active.

At night, red cellophane – the bees can’t see red light – can be placed over a flashlight for light.

Insecticide dust is preferred, but pressurized bee/wasp killer spray is also effective. Spray directly into the holes.

“I like the dust more. They are hairy and as they move through the tunnels, the dust will cling to them, causing them to die quickly,” Houseman said. “The liquid will dry and dissipate.”

Dust or spray once in the spring or early summer to eliminate adult bees. Dust or spray again in the early fall to kill the then-mature bees that were larvae in the summer. After the fall treatment, fill the tunnels with caulk and plug the holes with a glued wooden dowel, wood putty or more caulk.

If a non-insecticide method of carpenter bee control is preferred, wait until the adults have finished laying eggs and died in July. Get a metal wire that is rigid enough to jam through the larva cells and long enough to move all the way through the tunnels. Move the wire in and out of the tunnels several times. By puncturing the cells, the larvae will die.

Then plug the holes with caulk.

If larvae are left alive, they can mature into adult bees and bore out of plugged holes.

The bees will eat just about any type of wood but prefer soft woods such as pine, fir, redwood and cedar. Painting or sealing wood surfaces will discourage, though not fully repel, the bees from tunneling and nesting.

For more information on a variety of topics from MU Extension specialists and faculty, log on to http://extension.missouri.edu.