Sid Mullis: Stopping carpenter bees from boring holes in wood

I heard reports from some people about their first carpenter bee sighting about a week ago. That means we have about three or four more weeks to deal with their destructive behavior – boring into wood on or around our houses.


Most people call them bumblebees. Carpenter bees look very much like bumblebees, but we normally don’t begin to see bumblebees until later in the spring and summer. The difference in their appearance is that carpenter bees are blackish with yellow hairs and a shiny black abdomen. Bumblebees have yellow hairs on the tip of its abdomen (fuzzy). Bumblebees always nest in the ground, not in wood.

Each spring, though it seems that no wood around our houses or storage buildings is spared from the buzzing and, in too many cases, the boring. It seems the prime targets are wooden decks, overhangs and unfinished wood inside shop buildings. They also love old, wooden ladders.

Of all the wood out there, carpenter bees’ favorite seems to be redwood, cypress, cedar, white pine or Southern yellow pine.

Though carpenter bees prefer bare wood, they will attack seasoned or treated wood that has been softened by weather exposure. There is always the chance they will bore into pressure-treated or painted wood, but it is less susceptible.

The holes that carpenter bees bore are for making nests. The holes go about an inch deep into the wood, about two to four inches down the length of the board. They bore about one inch every six days.

Inside her gallery, the female bee gradually builds a large pollen ball that serves as food for her offspring. She deposits an egg near the pollen and then seals the section of the tunnel with a partition made of chewed wood. She constructs additional cells in this manner until the tunnel is completely filled, usually with six to seven cells (depending on the length of the tunnel).

The adult bees then die in a matter of weeks. The immature bees will stay in their tunnels until they emerge next spring.

Carpenter bees also can frighten people with their appearance.

The females do all of the boring, and thus all the work! The male hangs around outside and hovers about the head of any intruder. Although they are frightening because of their large size, the males cannot sting, so there is really no reason for you to be scared of them. The females can sting, but only when they are handled. Males can be distinguished from females by a whitish spot on the front of the face.

Swatting carpenter bees with a tennis racket might be a lot of fun and make you feel better, but that does little good in protecting the wood. Remember, it’s the females that bore and, in almost all cases, the females aren’t hovering around you. They are busy flying back and forth from the trees to the wood and aren’t paying you any attention.

Once carpenter bees find a home, populations will continue to get worse each year if you do nothing in controlling them because they return to nest at the same place.

To cut down on their numbers, you need to take some action on the females. It is difficult and can be time-consuming, but here is what you can do.

The first thing is to discourage their nesting by keeping your garage and any outbuildings closed when carpenter bees are actively searching for nesting sites. This normally occurs about mid- to late March, depending on when the temperature begins to warm up.

To kill and discourage the bees from boring, you can spray all the exposed wood surfaces that they might attack with an insecticide such as carbaryl (Sevin), or a synthetic pyrethroid (permethrin, cyfluthrin, bifenthrin, etc.). These last only one to two weeks, so you must spray two or three times while the bees are active.

Your next step (even if you didn’t spray before) is treating the nesting holes after mating season is over. Spray liquid Sevin or puff Sevin dust into the holes. A good can of Wasp and Hornet Spray (contains pyrethroid) also works well. Locate the holes and then come back around dusk and squirt or puff the insecticide into the holes. You might hear a buzzing sound (a good sign).

You will want to come back later and caulk the holes with wood putty. But don’t do this if you haven’t used the insecticide because next year, some bees will simply tunnel back out. Wait at least 36 hours (a few days is even better) after using the insecticide to caulk the holes. This will give the bees more time to contact and distribute the insecticide.

Remember, if you do nothing to the nest, you will continue to get a buildup of carpenter bees every year. Treat every nest you can find and you’ll see a dramatic decrease in their numbers next year.

Don’t worry about killing carpenter bees as far as nature is concerned. They are very poor pollinators of our plants. As a matter of fact, most entomologists consider them nectar thieves, taking the pollen and doing nothing good with it.




Sat, 02/24/2018 - 21:21

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