Carpenter Bee Facts

Details about the lifestyle and habits of the carpenter bee, and advice on how to get rid of them. October 4, 2007

Someone I know is building a barn. He had a bad experience with his last one with carpenter bees attacking the trusses. The local truss company exclusively uses SYP. So he has asked if we can mill him some lumber so he can make the trusses himself. He would like it to be a light/strong wood because it will be a remote location and transportation of equipment and materials is costly, not to mention labor.

No one mentioned carpenter bee problems when I was a kid. The only carpenter bees I ever saw were on nature programs on TV. Most of the barns around here were traditionally built out of oak frames and oak or tulip poplar siding. (Maybe those old-timers knew what they were doing?)

I'm looking for local (Kentucky) species that would suit the bill. I've read what I could find on the web about these critters, but there was no definite info on species that discourage them. There was one site that suggested they prefer soft, straight-grained woods. What local species are light, strong and carpenter bee resistant?

Forum Responses
(Sawing and Drying Forum)
From contributor M:
I don't know how to answer your question, but I thought I would share this interesting observation. I observed a carpenter bee in my newly constructed shop. It was going in and out of a hole in a board that I was using to brace my trusses when they were being installed. I looked closely and counted 3 holes in this one board. The interesting observation is that this board was ACQ treated to ground-contact specifications! I have not seen borings in my trusses or in the rough-cut SYP I used for framing.

From contributor K:
I am working on a job with a treated deck that has them. I have found them in eastern red cedar, and have seen them in western red cedar as well. All of these woods are highly resistant to rot and most insects. Since the bees are not actually eating the wood, the toxicity doesn't hurt them.

It might interest you to know that the bees that hover around the outside of the hole are the males, and are incapable of stinging you.

They usually enter the wood from the bottom, through a hole about 7/16", and then go up to about 5/8" after they are in, and turn and start tunneling down the length of the board. They may branch off several times, usually veering more toward the middle of the board, avoiding the outside.

They spend the winter in these nests in a state of hibernation. Maybe wood being a good insulator is the reason they stay away from the edges. If you were to hire an engineer to find a way to make wood lighter weight without hurting the strength, they would find a way to get rid of wood in the middle of the beam while keeping the top and bottom edges intact.

Since these bees are a great asset for pollinating flowering/fruiting plants, I think it would be a good idea to get over the fear, and appreciate them for what they are, rather than wigging out over them. This is especially important since there are parasites that are threatening the honey bees.

From Professor Gene Wengert, forum technical advisor:
The carpenter bees do not eat the wood. They are merely making holes for their home. This is why that treated wood does not kill them. They will attack any species; changing species will not fix the problem. They make rather large holes in the wood, so they quickly destroy the strength of a member that they are dwelling in. They must be eliminated promptly. You have a legitimate concern, so do not ignore them. The honey in their hive can weigh many pounds and can leak and cause subsequent damage too.

The cure is to insert a squirt of appropriate poison into the hole and then insert a wooden dowel into the hole. They will return to the same hole year after year, so the hole must be plugged. Contact your county extension agent for more details. Changing species will not fix the problem, although they do have a preference for wood that is a bit wetter than 10% MC, as such wet wood is easier to build a tunnel in, as it is weaker.

It is necessary to use a decay resistant and insect resistant wood species if the wood will be used in a damp location or be in contact with the ground. Yellow poplar does not have such properties. For trusses, you would want to use a strong species that has been graded so that you are assured of the strength of the members... This means that you will have to use a softwood species, such as southern pine. You can get this wood properly treated so it will resist decay and insects for a century.

From contributor R:
The previous response said that a carpenter bee will attack any species. With all due respect, I have never seen one go after oak (red or white).

From Professor Gene Wengert, forum technical advisor:
Given a choice, the bees will look for a softer wood, because it is easier to make a hole. However, they do infect oak from time to time.

The paragraphs below give more technical info on this insect including a way to tell the difference between a bumble bee and a carpenter bee. It is from the University of TN Extension.

by Karen M. Vail
Carpenter bees have been very active and residents have been alarmed by these large bees flying near eaves. Quite often it is the male carpenter bee that is seen patrolling the area and they are unable to sting. The females are not aggressive, but may bite and sting if handled. Males are easily distinguished from females by a large white marking on their “face”. So if you want to impress someone, reach up and grab one of those males hovering in your face.

Carpenter bees are large bees and are similar in appearance to bumble bees, except the dorsal (top) surface of the abdomen is almost devoid of hairs and appears to be entirely black in the carpenter bee. Also, don’t confuse the white-faced male carpenter bee with a bald-faced hornet which also has a white “face”. You’re most likely to encounter a female bald-faced hornet and she is not forgiving. Catching this female in your hand may cause her to sting, release an alarm pheromone and recruit hundreds of other nest mates - all with stingers.

While carpenter bees are pollinators for several species of plants such as may pop, they are considered pests when they bore into wood. Bare, unpainted, weathered softwoods, especially redwood, cedar, cypress and pine, are preferred. Painted or pressure-treated wood is less likely to be attacked. Some common nest sites include eaves, fascia boards, siding, wooden shake roofs, decks and outdoor furniture. A gallery for brood is excavated in weathered and usually unpainted wood and the exit hole is a nearly perfect circular hole about ½" in diameter. These holes often appear as if they were made by a drill bit. The gallery initially extends straight from the opening, but soon makes a right angle turn to go with the grain of the wood. In the gallery the female lays an egg, provisions it with nectar and pollen and seals the cell with chewed wood pulp. Galleries may contain six cells and are four to six inches long on average. However, because the galleries are reused and may be used by more than one bee, lengths of up to 10 feet have been reported. The new adults will appear in late summer.

Nonchemical or preventive controls include painting wood surfaces. Individual bees can be caught with a net and killed or swatted with a badminton racket. Also, a flexible wire can be inserted into the hole to kill adult and larval bees, but the wire needs to be strong enough to break the wooden cells and flexible enough to make the right angle turn.

Insecticidal dusts (Tempo 1D, DeltaDust, Zep Pest Termite and Ant Killer) can be puffed into nest holes in the evening when the carpenter bees are at rest. An insecticidal dust fills the void very well and will not soak into the wood as a liquid might. The bees should have access to the nest for at least 24 hours to allow them to spread the dust through the galleries. The hole is then sealed with a wooden dowel coated with suitable sealants, such as carpenter’s glue or wood putty, to prevent reinfestation, moisture intrusion and wood decay. Carpenter bees overwinter in previously used galleries, so the structure should also be inspected in the fall and any holes that may have formed should be treated and sealed.

In the past, many fact sheets referred to the use of Sevin (carbaryl) for control of carpenter bees; however, I have not been able to locate a Sevin label that listed wood as a use site. Ficam dust (bendiocarb) is very effective in controlling carpenter bees, but it has been voluntarily withdrawn from the market. Existing stocks can still be used.

Homeowners may not have access to insecticidal dusts labeled for wood treatment and thus may need to apply sprays (Bee/wasp killer aerosols, Ortho Termite and Carpenter Ant Killer [bifenthrin], Bayer Advanced Home Pest Control Indoor and Outdoor Insect Killer ready-to-use pump [cyfluthrin] or others) into the nest opening.

According to Mike Potter, University of Kentucky, a broadcast insecticidal spray onto wood surfaces attracting large numbers of bees may be needed as a deterrent. A broadcast spray, such as Bayer Advanced Powerforce Carpenter Ant and Termite Killer Plus Concentrate [â-cyfluthrin], Ortho Home Defense System/Termite & Carpenter Ant Killer [bifenthrin], or others), is often warranted when carpenter bees are riddling large areas of wood such as siding on a barn, wood shake roofs, or decking. A broadcast treatment is best accomplished with a pump up or hose end sprayer that targets the wood surfaces that are most favored by the bees (fascia boards, joist ends of redwood decks, etc.). Residual effectiveness of deterrent surface applications is only about 1-3 weeks, so the treatment may need to be repeated.

A few years ago, we were conducting carpenter bee research with the representatives from a local pesticide manufacturer and we needed to exclude the bees from currently occupied galleries in the fascia boards. On a warm sunny day in which we hoped all the bees would be foraging outside of the nest, the gallery openings in fascia board were stapled or nailed closed with gutter guard. Many bees became trapped behind the guard. Some were killed when attempting to forage, but many others from the next generation (last summer) were also trapped. Now, the gutter guards are not aesthetically pleasing. I believe they are a light, flexible, “woven” metal or plastic. An oil-based paint may provide some protection; however, if your fascia can be painted, why not apply the gutter guard and paint over it? No one will know it’s there, except the bees."

From the original questioner:
Thanks for your input. After posting this I realized that what I'm looking for is probably ephemeral. I read the info offered from ~ 10 sites. Most of the sites were universities, some were pesticide companies. Most of the sites agreed with what has been posted. In other words, there was no consensus. Most said carpenter bees would weaken the structure. But a few agreed with contributor K and provided anecdotal evidence to support their viewpoint.

There was one claim that several western species of carpenter bees would attack oak. But I'm not concerned about our local carpenter bees bothering oak. They seem to go for the easier stuff.

I also read many suggestions about treating the infested areas. Paints (oil or polyurethane based) and pesticides were the universal treatment. But all claimed the pesticide treatment wouldn't last more than 3 months to one year. So that seems like a feel-good solution to me. And, unless the trusses are painted before installation, painting trusses would be a hard job and it's no guarantee that it would completely stop them.

I've torn down a number of old barns. The only borer bee nests I found were in the pine boards. But I must admit I didn't look over the poplar or oak that closely. It's just that the pines had active infestations that caught my attention.

From contributor T:
I have been contemplating building bat houses to encourage higher bat populations around our property. We already see them at night but not in great numbers. We have a high mosquito population and carpenter bees too. I know the mosquitoes are active at night but I have never noticed the carpenter bees being nocturnal. If they are not, the bats would not help much with that.

I read the article you posted, Gene. One day a couple of weeks ago as I was working on the house, the bees were everywhere. I had the boys fashion a couple of thin staves with a paddle shape at the end and told them to have some fun.

This occupied them for hours. I have not noticed nearly as many bees since that time and they claim to have killed around 50 - 55 bees. Maybe it's all in my head but I hardly see one now. Maybe they are in their little holes, who knows, but there isn't anything close to the level of activity and visible population as there was before the boys went on their batting spree.

From contributor C:
I don't know if this will work or not, but maybe give it some thought. There is a product called Liquid Glass. I can't recall the exact scientific name. It's called silica something. It can be mixed with water, and then used for several different applications, such as sealing cracks in concrete. It is also fire resistant. It becomes very hard and has a clear finish. It might be possible to kill out the bees in the infested area of the wood, then plug their entrance holes. After that maybe try mixing some liquid glass up and either brushing a light coat on or spraying it through a pump-up sprayer. Liquid Glass is usually available at a pharmacy. It's not real expensive and comes in a quart jar. I think it has different mixture ratios for different applications. It might be just enough to keep them from starting to bore in to the wood.