Unlike the swarms and social hives associated with honeybees and wasps, there are many types of bees that lead specialized, solitary lives. Among these are the hunting wasp, the digger and mason bees, and the all too familiar Carpenter bee. These large, aerodynamic, hole-boring insects resemble bumble bees, but though similar in appearance, the two Apidae are separate species. Bumble bees are social and nest in the ground; the Carpenter bee excavates tunnels in sound wood to deposit its eggs, and therein lies the management problem.
One fine spring day, a homeowner goes out on the deck to relax in the sunshine and suddenly becomes aware that he or she is not alone. There is an industrious buzzing sound not unlike a miniature band-saw coming from inside the overhanging eaves, the deck floor is littered with drifting sawdust, and out of nowhere a large, shiny black bee has zoomed up close and personal in vigorous defense of the bore-hole that one is sure did not exist the previous afternoon. This is the Eastern Carpenter bee going about its life cycle, the male defending its territory (though he cannot sting) while the female (which can sting, though is usually not aggressive) drills tunnels in which she plans to lay her eggs. Xylocopa virginica’s battle lines have been drawn, and good luck to any resident Homo Sapien who tries to thwart the relentless strafing.
Carpenter bees will drill in any exposed wood but seem to prefer unpainted, weathered softwoods such as pine, redwood, fir, and cedar –the stuff of which siding, overhead eaves and trim, fascia boards, deck railings, windowsills, porch furniture, fence posts, and shingles are made, which is what makes them such a ubiquitous and challenging pest.
However, overlooking for a moment the annoyance and considerable structural damage that Carpenter bees can inflict, this tunneling activity is a marvel of insect engineering. The openings, which the female bores with her mouth parts, are a near-perfect circle measuring a precise half-inch in diameter. The bee drills straight up for an inch or two and then turns at a sharp 90-degree angle, usually along the grain of the wood, which she continues to excavate for another 4 to 6 inches or more.
At the end of the tunnel, the female then constructs a cell in which she deposits “bee bread,” a mixture of pollen and plant nectar, upon which she lays a single egg. Then she seals off the cell with a glue made from chewed wood pulp and repeats the process until 6 to 10 egg cells are constructed. After the eggs hatch, the bee bread nourishes the developing larvae until they chew back out through the cell walls and emerge as adults in late August or September, feed briefly in the open air, and reenter the tunnel galleries to pass the winter. Meanwhile, the adult bees that started this process die in July, their year’s cycle completed.
But for the homeowner whose dwelling seems to be turning into a bee-brick of Swiss cheese, that life cycle must be interrupted, or at least managed in an effective way. While successive generations of Carpenter bees may use previously-bored entry holes, they will drill new tunnel areas as their population expands. With repeated use, some nest galleries have measured as long as ten feet. To add to the headache, yellow jackets and other insects may take up residence in old Carpenter bee holes, or woodpeckers can decide to go after the hatching larvae and cause even worse damage to the wood. An integrated program of prevention and control has to be implemented as soon as possible, therefore, to head off a stream of cascading consequences such as these.
Exposed wood surfaces should be painted or stained and old bore-holes plugged as much as possible. Keeping garage and barn doors closed during springtime nesting season will deter some bee activity, at least in beams and wood surfaces inside those buildings. Then there is the Carpenter bee chamber, a type of glueboard trap with pre-drilled bore holes that attaches to soffits and facias. The bees enter the chamber, get stuck in the glue strip, and die. It is available at www.carpenterbeechamber.com.
The Organic Outlook
But as always when considering pest problems, the Carpenter bee exists in a wider natural context, of perhaps more importance now and in years to come than we realize. Carpenter bees play an important role in the pollination of wildflowers, grasses, and agricultural crops. With current declines in honeybee and bat populations, there is merit in considering management techniques that preserve the Carpenter bee wherever possible. In fact, English naturalists in the 19th century considered species of the Carpenter bee to be beautiful, and especially admired the variety known as the Violet bee, both for the color of its wings and the distinctive, complex concentric circles of egg-chamber tunnels that it cemented with glue made of meadow flower pollen and honey.
Also, it’s interesting to note that three Carpenter bees were part of 80 different science experiments (which also included harvester ants, silkworms, rats and spiders, and fish embryos) devised by school children from around the world and sent into space aboard the Columbia shuttle in January, 2003. The Carpenter bee project, set up and designed by students in Liechtenstein, was called the “Spice bees in Space mission” in reference to the Spice Girls pop band. The project was meant to discover what effect a lack of gravity might have on Carpenter bee construction habits, thereby gaining insights on how to build more efficient structures in space. Graphic design students created a mission patch with the shuttle Columbia and a Carpenter bee in flight above the earth. Later, the Liechtenstein government issued a commemorative stamp in honor of the students’ efforts.
Alas, the Columbia shuttle broke up on reentry February 1, 2003. All astronaut lives were tragically lost, along with an untold wealth of knowledge that might have been gleaned from those three Carpenter bees and all the other small and pesky creatures accompanying their human comrades on this journey from spaceship Earth.
- “Carpenter Bees,” Richard M. Houseman, Department of Entomology, University of Missouri Extension, posted 12/15/05.
- “Carpenter Bees,” Wm Michael Hood, Extension Entomologist, Clemon University, Clemson Extension Home & Garden Information Center, posted/revised April 2006.
- Bees, Wasps, and Hornets and How they Live, Robert M. McClung, Wm Morrow and Co., 1971.
- Peterson’s Field Guide to Insects, Houghton Mifflin Co. New York, 1970.