Carpenter bees get their name from their habit of drilling holes in dead wood. No big deal when they're digging away at a branch in the forest, but problematic when you've used that wood to build your porch, deck or entire house. Why do carpenter bees dig holes in wood? And what can you do to protect your house from carpenter bees?
There are hundreds of carpenter bee species around the globe. But, if you're reading this from somewhere in the eastern 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 a lot like the stereotypical bumble bee - big, black, yellow and fuzzy. As the name suggests, it is the most common carpenter bee in the eastern United States. But, while there are nine or 10 large carpenter bee species in the U.S., there are only two in North Carolina: 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 dead twigs and stems that have soft centers - but I won't go into them here.)
Why Do Carpenter Bees Drill Into Wood?
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 don't have queens and build colonies, like honey bees and other social insects do. Instead, they form loose social groups where up to five females may share a nest in the spring. However, when you see a carpenter bee drilling a hole, you are watching a female building a nest for her own offspring. They're not eating the wood, but excavating their nests with specially modified mandibles.
Once the nest is complete, the female will start collecting pollen and nectar, which she forms into a loaf in the back of the nest. She lays an egg and seals that space up with a mixture of spit and wood dust. 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.
How to Identify Carpenter Bee Holes
From the outside, the entrance to a carpenter bee nest looks like a small hole that is almost perfectly round. But there is a lot going on beneath the surface. A new nest might be only six inches long in its first year, but carpenter bees reuse and lengthen the tunnels so that over the years, they can grow several times that long with many branches.
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, with several bees tucked into a single nest together.
When warm weather returns, they spring back into action. The males usually emerge first and wait for the females to show up. You can spot the males because they have an ivory spot on their faces (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?
Unfortunately, you don't have a lot of options here. Carpenter bees 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 prefer softer wood (like pine), they will drill into whatever is available - including harder woods like cypress.
So, how can you prevent carpenter bees from putting holes in your house? There are three options, though they all have drawbacks.
One: you can simply swat them away from your house when you see them. Obvious, but effective - assuming you can hang around swatting bees away from your house all day.
Two: you can replace wood with composite materials or very hard woods (like black locust or ipe) the bees can't physically drill into. Very effective, but pricey.
Three: Some homeowners have reported success in reducing carpenter bee damage by applying various repellents to wooden surfaces or plugging nest entrances, although research has yet to back up any of these potential solutions. (NC State scientists are testing this approach - we'll keep you posted.)
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.
Note: Many thanks to Elsa Youngsteadt, associate professor of applied ecology at NC State, for taking the time to talk to me about carpenter bees. Any errors in the above post are mine alone.
