Springtime Bees and Sawdust

I recently came across a journal entry dated May 26, 2002. It reads as follows:

"This has been a second much-cooler-than-normal week here... It was like late October or early November, with chilly, toe-tingling mornings, brilliantly sunny, crisp afternoons perfect for gardening, low humidity... But it felt creepy. It was wrong, no matter how good it felt. I was thankful that this cold snap came in May and not in January, when I would have had to spend these days "hunkered down" in my sleeping bag...

"Large bees have been busy around my camp, despite the chilly weather. Actually, it’s kind of funny. Last week I told about the blown-over out house I’ve been dismantling, keeping part as building material and burning the rest. For this reason several boards are leaning against this or that corner of my outside kitchen as I decide what to do with them. Well, if a piece of lumber leans someplace for long, it’ll acquire a nest of bees, and then I feel bad about moving it, so it just stays there!"

"For the last couple of weeks little piles of sawdust have been appearing below everything wooden — below the scrap-lumber frame of my kitchen, below my fireplace elevated on wooden planks, and below all the out house planks. That’s because these bees have been excavating their tunnels. When they are building their nests, they chew holes in the wood about half and inch across, and in a day of chewing their holes grow about the same distance deeper, a bit deeper if chewing "with the grain." These days, the mother bees are busily entering their tunnels with large daubs of pale yellow pollen collected on their legs."

— Author Unknown

If you’ve also seen this insect, then you’ve also met the carpenter bee, Xylocopa virginica. At first glance, you might be tempted to call it a bumblebee because of its size, but it doesn’t seem to look or behave exactly as you’d expect. In fact, instead of flying low to the ground and moving fairly slow like a bumblebee would, these bees either hover motionless at eye level along wooden beams or quickly dart about. In addition, their bodies are shiny, rather than covered with the dense hair characteristic of bumble bees. If you are observant while outside working this spring, you’ll probably notice the presence of this large, distinctive-looking bee.

Carpenter bees are stout insects that have a metallic blue, green or purple sheen on their abdomens. They are not social insects, like their cousins the bumblebee or honeybee. However, they do build nests in which to live, lay eggs and rear their offspring. Some species are small, nesting in branches and small stems of trees. Others are large and prone to make nests in the exposed wood of homes, decks, etc. The entrance hole to these larger nests is perfectly round, about ½ inch in diameter, and goes straight into the wood. At a depth of about one inch, the tunnel turns at a 90-degree angle and follows the length of the wood. These tunnels are formed by the chewing activities of adult female bees.

Carpenter bees pass the winter inside their tunnels and emerge early in the spring to mate. Once mated, female carpenter bees make "bee bread." This is a mixture of pollen and nectar collected from flowers. She places bee bread at the far end of a tunnel, lays an egg on it, and then builds a wall from chewed wood pulp to seal off the cell. She repeats the process up to six times to form a row of cells containing eggs and bee bread within each tunnel. The eggs hatch in just two or three days. Each larva develops within their own cell, feeding on bee bread. After about two weeks, the larvae become pupae, which remain inactive for another two weeks inside the cell before emerging as new adults. New adults typically emerge late in summer and have a brief activity period before preparing for winter.

Males carpenter bees have a large yellow patch on the front of their faces, while females have completely black faces. In general, carpenter bees are not considered aggressive, although males are territorial and will hover in front of your face or buzz your head when you come into their territory. This behavior is convincing, but males cannot sting. Females are capable of delivering a painful sting, but unless provoked, they are reluctant to do so.

The damage caused by the nesting activities of a single pair of carpenter bees to structural wood is minimal. However, when numerous bees infest a structure over a long period of time, there can be considerable damage. Most damage occurs on decks, patios, fences, outdoor wooden furniture, etc. To manage these infestations, you can paint wooden surfaces or apply an insecticide to tunnel entrances before filling the holes. Several aerosol and dust formulations are available for use, but carbaryl (Sevin) or pyrethroid dusts are recommended. After applying an insecticide, wait for a few days before filling the tunnel with caulking material. This allows adult carpenter bees to use the tunnel freely and become exposed to the insecticide. If tunnel openings cannot be filled after a few days, repeated insecticide applications may be necessary at 2-3 week intervals during the summer season.

Please see http://muextension.missouri.edu/explore/agguides/pests/g07424.htm for more information about these interesting insects.

Richard M. Houseman, Department of Entomology, UMC (573) 882-7181