Who’s to blame, masons or carpenters?
When I was a kid my mom waged war on carpenter bees. She had purchased a circular picnic table made from thick redwood boards. The carpenter bees liked to set up shop on the perimeter of this table and drill straight in from the side. I remember my mom running outside with a flyswatter dozens of times a day, trying to rid herself of these destructive pests.
But I always kind of liked the holes. They felt as smooth as the inside of a seashell and were large enough to swallow my small finger. I thought they were cool because I couldn’t understand how a little bee could do that.
It turns out that carpenter bees use their mandibles to dig out and smooth the tunnels in which they will lay eggs. They do not eat the wood but may use the saw dust to build partitions between each chamber that contains an egg and a provision of pollen mixed with nectar. The holes are about a half-inch (1.25 cm) across and run 6-7 inches (15-18 cm) long. Sometimes more than one bee uses the main hole and each builds a tunnel that branches off inside the boards where you can’t see them. From a human point of view, this is probably not the highest and best use of your picnic table—but it’s really kind of awesome.
Carpenter bees will drill in trees, shingles, soffits, fascia, porch rails, eaves, decks, siding, and lawn chairs. They have preference for unfinished wood, but in a pinch will use pretty much anything they can find. Although most of the carpenter bees are solitary, they tend to live in proximity to each other, so you may see groups of them munching on your real estate investments, consuming your equity.
After the holes are drilled, the female provisions the nest, lays her eggs, and seals it up. The young emerge 5 to 7 weeks later and spend the rest of the summer eating, pollinating, and preparing for winter. Both the male and female bees overwinter as adults. Rather than drilling again, they clean out a previously excavated hole and hibernate there until spring.
Unfortunately, bees that nest in pre-drilled holes—such as mason bees—often get blamed for the holes that carpenter bees or other creatures build. Sadly, I’ve seen folks kill mason bees thinking they were responsible for the damage.
Carpenter bees are larger than mason bees; some are the size of bumble bees, some a bit smaller. But carpenters have a smooth—rather than a hairy—abdomen. Then too, bumble bees are often seen coming out of underground nests, whereas carpenter bees are seen hanging around wooden objects—usually treasured and/or expensive wooden objects.
The genus name for the nearly 500 species of carpenter bees is Xylocopa. According to Wikipedia this word comes from the ancient Greek for woodcutter. In the United States five species are prevalent, two on the east coast and three on the west coast. Both carpenters and masons are excellent pollinators so don’t kill either kind. If you have carpenters, provide some unpainted wood and try to guide them in that direction.