Later in the summer, goldenrod will be a favorite source of nectar for carpenter bees.
About this time each spring I visit a local village center, home to a lovely outdoor patio complete with redwood seating. These benches provide the perfect nesting site for large carpenter bees, and early May is a great time to watch an unparalleled display of aerial antics conducted by the male bees. Without fail, pedestrians who venture too near these wooden benches are dive-bombed by territorial male bees that jealously guard wooden benches, key nesting sites for their mates.
The small white patch on the face of this carpenter bee tells me it’s a male and that I have nothing to fear by getting up close and personal.
Watching humans duck and cover as male carpenter bees challenged intruders who dared to enter their territory was almost as entertaining as watching aerial battles among male bees. However, I did calm several patrons by explaining there was no danger of being stung. Male bees lack stingers and 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.
Female carpenter bees build galleries in wooden structures including benches, railings, mailbox posts, decks, and siding. Galleries bored into the wood 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 battle ensues. 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 afterwards, perhaps for more battles or romantic conquests, but the female bee had different matters to attend.
In the bustle of spring activities, even romantic encounters of carpenter bees are brief.
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 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, bees return to their galleries to spend the night after foraging all day. With the end of blossoms in the fall, carpenter bees return to their snug tunnels to chill out, protected from the ravages of winter.
A round hole chewed into a piece of wood provides access to the chambered brood tunnels inside.
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, several hundred 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.
In springtime, flowering trees like this Burford holly provide bountiful nectar for many important native pollinator bees, including carpenters.
References
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.