Friday, April 01, 2011

Carpenter bees work on wooden structures

As enthusiastic, bored children, we would try to hit them with baseball bats. A tennis racket would have been a better choice, but there were no tennis courts on our farm. Nonetheless, carpenter bees were a lot of fun for growing boys.

Adults, though, usually aren't into fun things like that. People who live in cedar-sided or log homes see no humor at all in these obnoxious bees. They just want to get rid of them.

About this time every year people see large, black bees hovering around their heads and homes.
They're probably carpenter bees. We get very little pollination benefit from them, but we do get some headache.

Look similar to a bumblebee

Carpenter bees resemble bumblebees but have a couple of noticeable differences. The upper surface of the carpenter bee's abdomen is bare, shiny and black. Bumblebees have a hairy abdomen with at least some yellow markings.

The other difference is where they nest. Bumblebees usually nest in the ground. Carpenter bees build their nests in tunnels they create in wood. They chew a perfectly round hole about the size of a dime into soft, untreated, unpainted weathered wood.

Male carpenter bees seem to be mean. But it's all an act. They'll hover in front of people who are near, even dive-bombing occasionally. But the males are harmless. They don't even have stingers.

Females hurt, damage most

Female carpenter bees do have stingers, though, and their sting can be quite painful. I had to be stung several times before I learned to leave them alone. The females seldom sting unless they are handled or disturbed.

Even if they don't sting, female carpenter bees aren't harmless. It's the fertilized females that excavate the tunnels and lay eggs in a series of small cells.

They provision each cell with a ball of pollen, on which the larvae feed until emerging as adults in late summer. The adults will overwinter in abandoned nest tunnels to return again the next year.

Prefer bare softwoods

Carpenter bees prefer bare softwoods, especially redwood, cedar, cypress and pine. They don’t typically bother painted or pressure-treated wood.

Common attack zones are eaves, window trim, fascia boards and decks. Sawdust beneath the hole is an easily recognizable sign of attack.

Control can be a combination of things. A fresh coat of oil-based paint is very effective. They don't like paint. Wood stains and preservatives are less reliable, but better than bare wood.

Where the bees have already attacked, spraying insecticide on the wood surface won't work. You have to inject it into each burrow to be effective. An aerosol spray for wasp and bee control will work if you direct it into the hole. Applications of cypermethrin or permethrin may provide short-term control when applied to wood surfaces, but will have to be reapplied after 1 to 2 weeks to maintain control.

Plug the hole

After a couple of days, plug the hole with a piece of wood dowel coated with carpenter's glue, wood putty or your choice of filler. This last step protects against future use of the old tunnel and reduces the chance of wood decay.

It's best to spray at night to kill the adults and the brood. If you spray during the day, the adults may be gone. And they may just start a new colony.

Remember, the females can pop you pretty good, so treating towards sunset or at night helps. Or you could make it a two-person job and arm the other with the tennis racket.

By B. Wade Hutcheson 

(Wade Hutcheson is a county Extension agent with UGA Cooperative Extension serving Spalding County.)

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