Carpenter bees can be hole-boring pests

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I saw carpenter bees for the first time this spring last weekend while working and spending time in my yard. 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 bumble bees. Carpenter bees look very much like bumble bees, but we normally don’t begin to see bumble bees 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. Bumble bees have yellow hairs on the tip of its abdomen (fuzzy). Bumble bees 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 around and in too many cases, the boring, 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 to attack.

The holes carpenter bees bore are for making nests. The holes go about an inch deep into the wood, and then the tunnel turns to go 2 to 4 inches down the length of the board. They bore about 1 inch every six days. Inside her gallery, the female bee gradually builds a large pollen ball which serves as food for her offspring. She deposits an egg near this pollen and then seals this section of the tunnel with a petition made of chewed wood. She then 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.

Unfortunately, they caused a lot of damage to a few stained, cedar boards on the front of my mother’s house in Blue Ridge, Ga. So last spring, before we could put the house up for sale, I had to replace several of them. The boards were only about ½ inch thick so the carpenter bees could not make nests after they bored. I wish they could have figured that out before they started boring but they didn’t.

In addition to the damaged wood, carpenter bees also cause major stress to people, especially young children, with their frightening appearance.

The females do all the boring – and thus all the work. The male hangs around outside and hovers around 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 them with a tennis racket may 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 in an area, 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 on the average 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 may attack with an insecticide such as carbaryl (Sevin), or a synthetic pyrethroid (permethrin, cyfluthrin, bifenthrin, etc.). These only last about 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 the pyrethroid) also works well. Locate the holes and then come back around dusk and squirt or puff the insecticide into the holes. You may 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.

Reach Sid Mullis, the director of the University of Georgia Extension Service office for Richmond County, at (706) 821-2349 or smullis@uga.edu.


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