The Washington Post
What to do about a carpenter bee infestation
Q: How do I deal with carpenter bees?
A: If you’re like many homeowners with a carpenter bee question, you’ve probably noticed round holes about 1/ inch
in diameter in siding, eaves, deck railings or other wood, and you’re worried about how much structural damage they’re doing. But if you’re also a gardener who loves the hum of buzzing and appreciates the crucial role that pollinators play, you may have delighted in seeing large but mostly black bees busy at work in your flower beds and vegetable gardens. These are carpenter bees in a different role.
Although they are too big to enter tubular flowers, such as penstemons, carpenter bees pollinate many flowers, including those of tomatoes and eggplants. And therein lies one of the problems about how to control them: You need to keep them from damaging your house, but you don’t want to kill them all off — especially now, when so many pollinator populations are in decline.
To figure out an effective strategy, it helps to understand a little about their lives and the tunnels they bore. Carpenter bees are roughly a similar size to bumblebees, up to about one inch long. There are many species of both types, but the best way to distinguish them is by their abdomens, the largest part of their bodies. Carpenter bees have shiny abdomens, often black, while bumblebees have hairy abdomens, often yellow.
Bumblebees typically nest in colonies in the ground and sting if someone comes near the nest, while carpenter bees nest alone in wood and rarely sting. Male carpenter bees can be very aggressive if you get close to their nests, but it’s all bravado: They don’t have stingers. The females do have stingers but rarely sting unless attacked.
Because carpenter bees don’t form colonies or have a caste system with queens and workers like honeybees or bumblebees do, they are classified as solitary bees. But they are far from being loners: If you have one, you probably have many, because the kids tend to hang around in the same place as the parents. In a natural environment, they bore into dead but not decayed trees. In homes, they are often in siding, deck railings, eaves or fascia boards. Unlike with termites, you usually don’t need
to worry that they have tunneled into framing or floor joists, because carpenter bees typically stay in wood that’s on the exterior surface. The holes you see go straight into the wood, but only for an inch or so, then take a turn and follow the wood’s grain lines.
Male and female adults overwinter in tunnels that were used for the previous season’s egg-laying. They emerge in spring and mate. Then the females extend existing tunnels or bore new ones, using their mandibles, or mouth parts. With the male guarding the hole, the female makes multiple trips to provision the end of a tube with a ball of “bee bread,” a mixture of pollen and nectar. On that, she lays a single egg, then walls off that cell with chewed wood pulp. This process is repeated about five to eight times, with the adults resting in the tube overnight before resuming work the next day.
The eggs hatch, and the larvae develop out of sight, feeding on the bee bread. Later in the summer, the new bees emerge and fly about the garden until the weather cools and they find an empty tube where they can overwinter and begin the process again. Female carpenter bees often live for several years, while
males die after about a year.
The first year a tunnel is used, it might be only four to six inches long, which doesn’t weaken the wood significantly, although the hole can let in water, which can lead to rot. But when a tunnel is used and extended year after year, it can go much longer, up to 10 feet, according to a flier from Clemson University. These yearly additions can weaken the wood, especially if other bees bore tunnels into the same piece.
So how do you keep them from doing that? Carpenter bees almost always tunnel into bare wood, so painting exterior wood is one of the best longterm solutions. But if the bees have already been chewing on your house, you can’t just plug the holes and paint. You need to replace the wood or kill the bees hiding in the tunnels first, because any live bees left inside can chew their way out. If you don’t want to replace the wood or use pesticides, it might be possible to trap the bees, plug the holes, then look for new holes and keep trapping and plugging until no more holes appear. But you’d need to commit to frequent inspections.
If you opt for trying to eliminate the problem in one sweep, effective pesticides include sprays and powders, which you should apply just where they will target the bees in the tunnels in your house. An aerosol spray that foams or has a straw tip is much easier to use in a targeted way than a liquid that you dilute and apply with a garden sprayer. Spectracide carpenter bee and groundnesting yellow jacket killer ($5.47 for a 16-ounce can at Home Depot) is one example of a foam product.
To apply powder in the holes, use a device with a small bellows and wand, such as the bellow hand duster ($14.98 from
domyown.com). The site sells a couple of different powders, because states vary in what is legal to use. Retailers should be selling only what is allowed in your state. You can also do a Web search for your state and the words “carpenter bees” and “extension,” to get advice vetted by your state’s land-grant college or university.
After you treat a hole, wait 24 hours, then plug the hole with a short length of wooden dowel coated with wood glue or with steel wool covered with caulk. Or you can use push-in products, such as Trebor’s plastic plugs ($6.08 for a package of 20 from
Treat the holes in the evening, when the bees are in the tunnels. If the holes are hard to reach or if your schedule might keep you from plugging the holes 24 hours after you treat them, consider hiring a pest-control professional. Make sure you talk through their process, though, and ensure they don’t plan to spray wide areas, which could harm other insects. The pesticides labeled for use against carpenter bees can also kill other insects.
You can also purchase a trap, such as the Beesnthings outdoor bee trap ($19.98 at Lowe’s). Or you can make a trap by building a box about five inches on all sides out of wood. Drill 1/2-inch-diameter holes into two sides that slant slightly upward. Into the bottom, drill a hole sized for the neck of a plastic water bottle. Twist an empty bottle into the hole, and hang the trap near where the bees are active. Bees can then fly in, fly toward the light coming through the bottle below and not be able to find their way out.