Next time you are dodging carpenter bees, take a moment to check out their head. I’ll bet you will find a white patch on its face between its eyes, the hallmark of the male carpenter bee.
A week or so ago, during a Q and A session at a meeting, I was asked by one nature enthusiast why large black bees were bombarding him in his back yard. Without fail, about this time each spring humans who venture too near a child’s wooden play set, wooden benches or railings, mailbox posts, decks, or houses with cedar siding are divebombed by territorial male bees. The bees have nothing against humans. They are simply jealously guarding potential wooden nest sites from interlopers. Interlopers include other male carpenter bees or almost any other creature that comes into range, including humans.
Wooden structures like this play set bear telltale damage as woodpeckers search for carpenter bees inside the wood. Male carpenter bees zoom around nearby sensing that nubile female bees will soon emerge from these galleries. They divebomb other competing males and nosy humans, aggressively defending their mating territory. When females emerge, they will quickly be mated by diligent guy bees patrolling nearby. Once inseminated, females build new galleries in wooden structures creating nesting sites for their young.
On the outside of a piece of wood all you see of the carpenter bee’s handiwork is a perfectly round hole.
Why do they do this? Here’s the deal. Female carpenter bees build galleries in wooden structures to serve as nurseries for their young. Male carpenter bees go to great lengths to convince potential mates of their worthiness by selecting and defending prime nesting sites. When other male carpenter bees approach defended territories, remarkable aerial battles ensue. Swooping, grappling, and biting often result in both combatants tumbling to earth before one withdraws from the fray. I watched one victorious male guard a nesting site and soon a lovely and somewhat coquettish lady carpenter bee arrived. She rested on the wooden bench guarded by her suitor and a short but energetic romantic interlude ensued. As far as I could tell, the male flew off somewhere, perhaps for more battles or romantic conquests, but the female bee had different matters to attend. After mating, the she bee begins the task of excavating a hole in the wooden structure to be used as a nursery for her brood. Her powerful mandibles create a slightly oval to almost perfectly round hole as she penetrates the wood to the depth of about a half inch. She then makes a right angle turn and continues tunneling parallel to the grain of the wood excavating a series of brood-cells in a linear tunnel. In a piece of wood removed from one of the benches, I observed several tunnels more than a foot in length, some of which branched into secondary galleries. Each tunnel contained as many as thirteen individual brood-cells.
But on the inside, you can see a gallery of brood chambers carved into the wood by the mother bee for her babies.
To construct each multichambered gallery represents more than a month’s worth of chewing and one has to admire the determination of these industrious gals in excavating a home for their young. After the chambers are built, they are meticulously cleaned and filled with bee bread, a nutritious mixture of pollen, nectar, and secretions from glands on the female’s body. Bee bread serves as the food for the young carpenter bees. Starting at the end farthest from the entrance the female deposits an egg in each brood-cell. Each egg hatches into a legless larva that eats bee bread and develops during the course of spring and summer. In brood-cells furthest from the entrance, older larvae complete development first, pupate, and then after emerging from the pupal case in late summer these new adults push their way past brothers and sisters to escape the gallery and search for nectar and pollen. As summer wanes and autumn waxes, newly minted bees forage during the day and return to their galleries to spend the night. With the end of blossoms in the fall, carpenter bees return to their snug tunnels to chill out until the following spring, protected from the ravages of winter.
On a chilly dewy morning in spring don’t be surprised to see a male carpenter bee (left) and a female carpenter bee (right) resting on a flower head.
In locations where carpenters are present, watching humans duck and cover is almost as entertaining as watching aerial battles among male bees. Male bees lack stingers and although the gals are equipped to sting, I have never been stung by one nor have I heard of anyone who was harmed by these fascinating creatures. Carpenter bees do cause some damage to wooden structures. And once woodpeckers find a structure housing carpenter bees, they get busy and can do some remarkable destruction as they peck holes in the wood searching for carpenter bee babies for dinner. Nonetheless, these entertaining native bees provide important services by pollinating our trees, shrubs, and crops.
At past events such as Maryland Day at the University of Maryland at College Park, which will be held on Saturday, April 26 this year, a thousand or more people visit our Insect Petting Zoo. At the zoo our resident carpenter bees receive much interest and attention. In years past, several children and a few courageous adults held male bees and were fascinating by the buzzing sounds and vibrations generated by flight muscles that power their wings. In discussing the antics and activities of carpenter bees, I was heartened to learn that most folks take a “live and let live” approach to dealing with the carpenters. As one lady put it, “This is their world too, you know.” I do know, and well said.
Acknowledgements:
Special thanks to Frank Bruno and the folks at the Howard Conservancy who served as the inspiration for this episode. “Bionomics of large carpenter bees of the genus Xylocopa” by Gerling, Velthuis, and Hefetz” was used as a reference for this Bug of the Week.