Carpentry bees can be deterred from destroying wood


Many years ago a neighbor approached me with the question of how the carpenter bees are busily working their way into the moldings on his veranda. We had never met before. He was something of a hermit, but he knew of my interest in the backyard nature and was excited to show me these beautiful, giant bees. Carpenter bees and bumblebees are the largest bees in North America. I had never met carpenter bees before, so this day marked the start of two wonderful friendships.

Carpenter bees have a bad reputation. Their common name – carpenter bee – comes from their habit of digging round tunnels in wood. They do not eat the wood, but rather chew dead wood (trees, wood paneling, timber, fence posts, etc.) to build branching galleries for their eggs. Uncontrolled, this tunneling behavior can cause considerable damage to a house, as the enormous amount of energy required to create these tunnels means that bees prefer to reuse and expand existing tunnels rather than opening new ones.

As I went to the bees, my neighbor showed me the perfectly round entrance holes that were drilled (actually chewed) into the wood paneling around his porch. As we got closer, the big bees hovered right in front of us and bombed as we got closer. As we reversed, they followed us and continued to hover at eye level until we were a safe distance away. The message was clear: they wanted us to withdraw. These were most likely male carpenter bees. They become very aggressive to defend their mating area but lack spines so they are all bluffing. I’ve never seen this myself, but I’ve read that carpenter bees encounter intruders in order to scare them away. Female carpenter bees have spines but rarely use them, even to defend their territory.

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A male carpenter bee can be recognized by the white spot on its face.

I’ve come across carpenter bees over the years since that first meeting, but we’ve seen a lot in our garden this summer, hopefully as a result of our goal of creating as biodiverse pollinator garden as possible. I hope it’s not because they discovered our big old barn made of lots of beautiful softwood to tunnel into. I wanted to double-check my identification of these rather obviously large bees (I was a little concerned that it was actually some type of bumblebee) and asked Dr. James Dill, the Pest Control Specialist at the University of Maine Cooperative Extension, came to see my pictures. He confirmed they were Eastern carpenter bees (Xylocopa virginica) and gave some tips on how to tell them apart from bumblebees.

You can recognize a carpenter bee by its completely black face.  The males have a white spot on their face.

According to Dill, one of the most important traits that differentiate them from one another is whether or not they have hair on their stomach. Bumblebees always do. They are hairy everywhere. Carpenter bees almost always have no stomach hair. Only her chest is hairy. Carpenter bees also have a shiny black spot on the back of their rib cage. Don’t bumblebees.

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One of the things that make carpenter bees stand out is the shiny black spot on the back of their rib cage.

Despite the potential for wood damage, carpenter bees are pollinators that you really want to have in your yard. They feed and pollinate a large number of different wildflowers and agricultural crops. They are also extremely efficient pollinators. They use a technique called buzz pollination, where they use their powerful pectoral muscles to vibrate to shake the pollen out of the anthers, making it more accessible for collection.

Carpenter bees are furry on their yellow rib cage but hairless on their black abdomen.

My neighbor’s question was how to keep the bees out of the stock without resorting to pesticides. He considered it a crime to intentionally kill pollinating insects (I agree). Fortunately, there are several approaches that don’t involve pesticides. Sometimes just painting or staining wood keeps them from starting digging. Holes can be filled at the end of the season to keep the returning bees. Softwood blocks (they prefer pine over hardwood) can be placed nearby as an attractive alternative to your home. I have one in my garden in the hope that some carpenter bees will call it home (unfortunately no excavation yet) so that I can follow their tunneling activities more closely. Pesticides should be used as a last resort, if at all. Pollinating insects are declining everywhere. We need our bees.

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Susan Hecht

Susan Pike, environmental science and biology researcher and teacher at Dover High School, welcomes your ideas for future running hours. She can be reached at [email protected] Read more about her Nature News columns online at Seacoastonline.com and pikes-hikes.com and follow her on Instagram @pikeshikes.

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