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Q. Carpenter bees have ruined the framing around my garage door. They are back again this year. If I plug up the holes won't they drill somewhere else?
A. Maybe, but there are steps you can take. Carpenter bees are not considered "wood destroying" insects on the same damaging level as termites or carpenter ants but if they pick your place to take up residence they sure can be an annoyance. They are just big bugs that look like bumblebees but don’t make honey. They're called carpenter because they leave little piles of sawdust under where they are working like a human carpenter would using a saw on a board dropping the dust just under where the cut is m ade.
The males do not sting but the females will sting if handled roughly. Their resemblance to bumblebees is close. Bumblebees have a hairy abdomen with some yellow markings but I’d only examine a dead one for identification. Bumblebees live in the ground. The only difference between the two for our purposes is behavior.
It’s the females that the cut perfect holes, about 3/8ths of inch in diameter, into raw or stained wood or on wood that the paint film is thin or damaged. They love cedar but any trim or siding of natural softwood wood will do for them. They turn 90 degr ees after they've bored in about a 1/4 or 1/2 inch into the board and chew a chamber into the wood along the grain for about 4 to 6 inches for a brood chamber-- all at the diameter of the surface entry hole. There they deposit larvae sealing them up in the end of the chamber with a paste of chewed up sawdust, pollen and bee spit. April and May is the time of year that they do this, that’s why you’re seeing them now. The larvae that they deposit in the chambers takes from one to three months to mature, then out they come-- full grown carpenter bees. Expect to see them again in late summer.
Sometimes the bees will re-use old chambers rather than make new ones but even though the boring that they do tends not to severely damage the structural integrity of the wood in question, I've seen roof trim boards that look like they've been shot at wi th a pistol with many perfectly round bee holes like the ones on your door trim.
You'll see carpenter bees buzzing about the boards and flying around and diving fast in an aggressive manner. The males doing this can't sting but are hoping any potential predators of the larvae they are protecting don't know that. It works on me and I avoid any diving bee but woodpeckers apparently prize carpenter bee larvae as a delicacy. If the unlucky combination of a carpenter bee infestation coupled with a woodpecker discovery takes place at your house, the woodpeckers will punch some nasty hol es into your wood trim looking for lunch and will make a racket doing it. Now your wood trim will really get damaged.
The most common approach to carpenter bee control is to seal the holes and paint the wood. Some suggest dusting the holes with Sevin®. If you use caulk on the holes and it's soft they will bite right back through it so the best stuff to use is plastic wood which, if you've ever used it, you know gets harder than the wood itself. The other commonly used wood putty--water putty-- will work too.
The paint surface must be a true surface film and not merely a wood stain. This presents a dilemma to some as one of the most popular woods with both carpenter bees and homeowners alike is cedar and cedar looks best stained.
I've heard of stuffing the bee holes with steel wool or nailing common window screening over the holes to discourage these bees. Wrapping the trim with vinyl or aluminum is a drastic but successful tactic. If you get into wood replacement be sure that you paint the wood well before putting it up-- that's for both bee and rot protection.
An infestation is normally a small population. I Have a friend who went after his problem with a pool net and when he was done only counted about 15 dead bees. Flying wasp sprays are effective but you've got to chase them around squirting poison at them to actually kill them.
Carpenter bees are known as good pollinators. A good argument for them these days as the honeybee population is mysteriously declining. Other than the holes they don't really hurt anyone so my advice would be to plug, caulk and paint.