Guardians of the galleries: Male Eastern Carpenter Bees, Xylocopa virginica
On a chilly dewy morning in spring don’t be surprised to see a male carpenter bee (left, with a white spot on its face) and a female carpenter bee (right, no white spot) resting on a flower head.
About this time each spring, wooden structures in the DMV provide opportunity to witness an unparalleled display of aerial antics conducted by male carpenter bees. Frequently, humans who venture too near children’s wooden play sets, benches, railings, mailbox posts, decks, and houses with cedar siding are divebombed by territorial male carpenter bees that jealously guard key nesting sites for their mates. Carpenter bees resemble bumble bees in size and appearance, but notably have a glossy black abdomen rather than the hairy body sported by the bumble bee. Female carpenter bees build galleries in wood 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 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.
On the outside of a piece of wood all you see of the carpenter bee’s handiwork is a perfectly round hole.
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. To construct each tunnel 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 and after emerging from the pupa 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, after foraging all day bees return to their galleries to spend the night. With the end of plants blossoming in the fall, carpenter bees return to their snug tunnels to chill out, protected from the ravages of winter.
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.
But on the inside, you can see a gallery of brood chambers carved into the wood by the mother bee for her babies.
Watching humans duck and cover as male carpenters challenged intruders who dared to enter their territory is almost as entertaining as watching aerial battles among male bees. However, male carpenter bees lack stingers and are therefore unable to sting. Although the gals are equipped to sting, I have never been stung myself nor have I heard of anyone who was harmed by these fascinating creatures. Carpenter bees do cause some damage to wooden structures; however, these entertaining native insects provide important services in pollinating our trees, shrubs, and crops. At past events such as Maryland Day at the University of Maryland at College Park (to be held this year on April 29), over a thousand people visit our Insect Petting Zoo, and our resident carpenter bees received much interest and attention. Several children and a few courageous adults held the male bees and were fascinating by buzzing sounds and vibrations generated by flight muscles that power the 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 know, well said.
Acknowledgements
Special thanks to John Davidson for sharing good carpenter bee stories with me. “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.
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