Bad Bugs of Summer: Carpenter Bees

Our first two posts on the bad bugs of summer were about bloodsuckers: mosquitoes and ticks. We’ll now look at a pest that is a plague on our homes, if not our flesh – carpenter bees. However, in keeping with tradition, this “bad bug of summer” is not a true bug.

Why are carpenter bees bad? Because they drill holes in dead wood. Not a problem if they’re chipping away at a stump in the forest, but problematic when you’ve used that dead wood to build your porch, deck or entire house. Having lots of holes in your porch is, frankly, not ideal.

There are hundreds of carpenter bee species around the globe. But, if you’re reading this from somewhere in the continental United States, odds are good that you think of Xylocopa virginica when you think of carpenter bees. Commonly known as the eastern carpenter bee, virginica looks exactly like the stereotypical bumble bee – black, yellow and fuzzy. As the name suggests, it is the most common carpenter bee in the eastern United States. But, depending on who you ask, there as many 20 different large carpenter bee species in the U.S. In North Carolina, there are only two: virginica and Xylocopa micans, also called the southern carpenter bee. (There are also so-called “small carpenter bees.” From the genus Ceratina, these species drill into soft-stemmed plants – but I won’t go into them here.)

Do carpenter bees eat wood, like termites? Nope. Are they building colonies in your deck? Nope. So what the heck are they doing? Glad you asked.

Carpenter bees are so-called “solitary” bees. They don’t have queens and build colonies, like honeybees and other social insects do. When you see a carpenter bee drilling a hole, you are watching a female building a nest solely for her offspring. They’re not eating the wood, but chiseling out their nests (which can be six to 18 inches deep) with specially modified mandibles. Once the nest is complete, the female will shove in a ball of pollen, lay an egg and seal that space up with a mixture of spit and wood dust or whatever’s handy. She’ll repeat this process until she has laid all her eggs – each of them lined up and sealed in their own chamber within the nest. A pollen ball is in each chamber to give her offspring something to feed on when they hatch from the eggs as larvae. Once the eggs are laid, the female hangs around for a bit and then dies.

You’ll see this nesting behavior (also known as: “annoying hole-drilling behavior”) in late spring and early summer. In late summer, the offspring will begin to emerge from the nest as adults. They pretty much just fly around, eating and hanging out. They don’t drill any new holes (yet). When the weather gets cold, they’ll set up shop in existing holes to get through the winter.

When warm weather returns, they spring back into action (pun intended). The males usually emerge first, and wait for the females to show up. You can spot the males because they have a white spot on their heads (also, like all male bees, they can’t sting). When the females emerge, they mate and the males die off. Then the cycle starts again: drill hole, lay eggs, die.

What can you do to protect your home from carpenter bees? Not a lot. They will drill into any type of dead wood (like your deck), and treating your wooden porch, deck or siding with paint or pesticides isn’t really effective (since the bees don’t eat the wood). Also, while bees do prefer softer wood (like pine), they will drill into whatever is available – including harder woods like cypress.

That leaves three options. One: you can simply swat them away from your house when you see them. Obvious, but effective – assuming you can hang out swatting bees away from your house all day. Two: you can replace wood with composite materials the bees can’t physically drill into. Very effective, but pricey. Three: you can try to lure them away from your porch by giving them a more attractive alternative. For example, build a wooden trellis some distance from your house, and cover it in flowering plants. There’s no guarantee that will do the trick, but – worst case scenario – you’ve now got a nice trellis.

In any event, like most bees, carpenter bees consume nectar and pollen from flowering plants. This means that they’re effective pollinators – something we could use more of. So, try not to kill them if you can avoid it.

Check out the other posts in our series on summer pests: mosquitoes, ticks, horse flies and black widows.

Note: Many thanks to Dr. Mike Waldvogel, extension specialist and associate professor of entomology, and Dave Stephan, insect identification specialist, at NC State, for taking the time to talk to me about carpenter bees. Any errors in the above post are mine and mine alone.