Tim Lockley: Carpenter bees' damage is mostly cosmetic

By Tim Lockley

"Beware the Ides of March!" Caesar would have been better off if he had heeded the words of the soothsayer. So would a male carpenter bee I came upon on the 15th of March.

Whenever I make it home for lunch, I walk my younger daughter's dog We take a quick turn around the neighborhood and then return home where she relieves herself (the dog, not my daughter) in my yard. Since the beginning of March, as we passed by one certain spot, a male carpenter bee has buzzed by us. On the 15th, it threw caution to the wind and flew too close to my daughter's dog. A quick snap, and bee was no more. Fortunately, although male carpenter bees can be quite aggressive, they have no sting, so all the dog got was a little more protein in her diet.

Except for their tendency to carve out a place for their children in wood we want to preserve, carpenter bees are the good guys. With the decline of honey bees in recent years, many of us have had to rely on pollinators like carpenter bees to take up the slack. They've been given a bad name because of their tendency to use our wood for their brood cells, but they really cause nothing more than cosmetic damage. It takes a large number of carpenter bees a number of years of repeated colonization to actually cause structural damage. Woodpeckers are more likely to do more damage to your home than carpenter bees. Of course, this doesn't stop people from panicking when they see the sawdust starting to pile up.

It's the females that do the boring. They chew a 1-centimeter (half-inch) round hole in a protected spot. She'll bore in 5 centimeters (2 inches), then take a 90-degree turn inside the wood. She then establishes a series of cells along a tunnel from 10 to 15 centimeters (4 to 6 inches) in length, some times longer, along the grain of the wood. The male stays outside the brood cells, bringing the female food and guarding her nesting site. Inside the tunnel she's made, the female places large pollen balls, which serve as food sources for her offspring. She'll deposit one egg for each pollen ball, then seal off each section with a thin wall of chewed wood. The female lays additional cells in this manner until the tunnel is completely filled. This usually means six to seven cells. The last egg laid is the first to hatch; were it the other way around, the young carpenter bee at the end of the tunnel would have to bore through the other cells to emerge from the nest. After laying her eggs, the mother dies in a few weeks. The larvae develop in five to seven weeks and new adults emerge in mid- to late summer.

To keep carpenter bees from chewing up your wood, you have to keep exposed wood surfaces painted or stained. If the bee can't figure out if it's wood, they won't waste their time trying to bore into it. If you find any holes bored by the bees, run a pipe cleaner or other flexible wire into the gallery. This will puncture the cells, exposing the larvae to the environment, where they will die. Seal up any galleries that have been formed, using caulk or liquid wood. Treating each nest with insecticide can be somewhat labor intensive, but it will work over time. A better method may be to apply a wood treatment such as Tim-Bor. This particular pesticide is borate based and is designed to keep wood-boring insects from getting into wood.

If you can tolerate a hole or two they make in your wood, I say leave the carpenter bees alone. Their ability to pollinate our gardens more than makes up for the little damage they might do.

Tim Lockley, a specialist in entomology, is retired from a 30-year career as a research scientist for the U.S. Department of Agriculture. For answers to individual questions, please send a stamped, self-addressed envelope to Tim Lockley, c/o Sun Herald, P.O. Box 4567, Biloxi MS 39535.