JOHN THE OBSCURE ™
By John Ruch
© 2006
The Bumblebee’s Shiver: Secret Sonic Powers
of the Other Buzz
It’s a shame that most people use nature as a place to jog with an earful of iPod, let their dogs run illegally off-leash, drink cheap beer where Mommy and Daddy can’t see and/or drive an ATV through the heart of it—in short, to continue paying attention only to themselves.
With a mere minimum of awareness, you can often walk smack-dab into the grand mysteries that are always closer than we realize. For example, the little-known sonic weaponry of bumblebees.
Such was my pleasant fate to discover last week during an exploration of a beautiful garden cemetery near my home. Walking by a group of rhododendron bushes in full flower, I paused, because on that gray day the purple blooms appeared to almost glow, as if shimmering or blurring into the atmosphere. “They look ultraviolet,” I thought, and then quickly corrected myself that they are ultraviolet in at least part of their coloration, which is why bees, which see into and are attracted by such wavelengths, were patronizing the blossoms.
I decided to look at the bees, mostly bumblebees—warily, as I have a horrifying history with them, including a half-dozen attempting to nest in my hair when I was a young child. I thought blandly that the big, furry bees are cute, especially when they fold their relatively small wings down and crawl about.
Watching a bee enter a flower to feed on the nectar and gather pollen, I heard it emit a high-pitched, even buzz akin to a dentist’s drill or a mosquito in the ear. Unlike the familiar bee buzz, it was not produced by the wings, which remained folded and motionless. This other buzz was of a much higher pitch, as well, and seemed to come from the head area, though it otherwise sounded similar to the regular buzz.
I was able to hear two bees producing this sound several times each. Frequently they would enter a doubled-over or semi-curled position while making it.
It was a small sound, easily drowned out by the normal buzzing of other bees nearby or even an incoming plane overhead.
I had the fancy that it was some sort of bee-talk, the apiary version of a child endearingly humming to herself while munching her lunch. But of course, all I really knew was that I had finally noticed something about bees that had somehow escaped a lifetime’s experience.
Some of the world’s top bee experts have since been kind enough to explain that what I heard was something far more remarkable than my feeble imaginings: “sonication,” the bees’ ability to shiver their muscles so quickly they emit vibrations powerful enough to knock pollen out of a flower, compact soil in their nests and scare the hell out of enemies a la rattlesnakes. The bees become, in the words of sonication expert Stephen Buchmann, “living tuning forks.”1 Amazingly, these vibrations involve the wing muscles without the wings moving at all—the muscles are actually detached from the flight mechanism to create the buzz.
Specifically, I was observing “buzz pollination,” which is sonication applied to anthers inside a flower to shake the pollen loose. Several common plant families have anthers that have evolved, possibly in conjunction with the bees, to release pollen only through small holes in response to vibration, “like a salt or pepper shaker,” as York University biologist Laurence Packer put it.
That includes such valuable crops as tomatoes. It’s long been known that tomato flowers need a good shake to pollinate. Indeed, you can still buy the sort of electric buzzers that greenhouse tomato workers used to wiggle plants with back in the day. At www.hydro-gardens.com, you can pick up the Pollinator II, which looks like a pen with a stick coming out the end, for $15.95 (AA battery not included), or drop $175 on the Ultima Pollinator, a heftier block-like device with a 6-volt battery. (Buchmann says a middle C, 512-hertz tuning fork will give you similar results.)
But the
real “ultima” pollinator is the bumblebee. Long
uncultivated because they don’t produce much honey, bumblebees over the past 15
years have been domesticated for use in tomato greenhouses. They’re perfect for
the job, and work only for food. “Now, there’s a multi-million-dollar bee
industry,” says Jim Cane, a research entomologist at
In buzz pollination, the bee grabs the flower, often the stamen itself, and may bite into it as well. Then it shivers its indirect flight muscles, possibly hundreds of times per second, in an oscillation that Cane describes as perfect isometrics. Loud enough to be heard by me a yard away, this buzz causes a cloud of pollen to be ejected and get all over the bee due to electrostatic forces and its own gathering, as Buchmann described it.
That curling position I noticed—the “characteristic ‘C’ posture”—may be so the pollen gets onto the bee better (the anther is often pressed directly under the insect), though it may also be a function of the muscle contractions involved.2 In any case, I heard the buzz without seeing any curling in some instances.
Interestingly, rhododendrons are an oddity in the buzz pollination world. They indeed have pollen that plays hard-to-get, releasable only through tiny pores. And yet, bees rarely sonicate them. I not only witnessed a fairly hard-to-spot behavior, but I did so in a very unusual circumstance. It’s unclear why bees don’t often sonicate rhododendrons; the pollen may eject under normal environmental movement and then stick to the anther for bees to collect.3 On a return trip today, I was unable to hear any bumblebees sonicating, though conditions had changed as well; the blossoms were wilting and many had fallen, and honeybees now greatly predominated over bumblebees. (Cane notes that bumblebees will sometimes sonicate a regular, easy-to-get flower just to get the pollen even faster.)
And honeybees, for all their many virtues, do not sonicate. Many other types of bees and wasps do, however—though bumblebees are known as the best, especially because of our financial interest in their pollination efforts. (Cane said each species has a characteristic frequency and duration, enough that he and his fellow researchers have been able to identify bees by their sonications in the field with their backs turned.)
The insects use their sonic super-powers for a variety of tasks. Bumblebees, which sometimes live in underground burrows, may use it to compact the soil in their homes, or loosen a pebble blocking a tunnel by grabbing it and giving it a sonic blast. Mud dauber wasps, which build their nests out of clay and mud, may use sonication to liquefy and smooth out the material, according to Cane.
Despite its name, sonication usually isn’t intended to produce sound per se, in the sense of vibrations moving through air. Instead, it produces vibrations through solid materials the insect is grabbing—a semantic distinction, but important considering the terminology.
However, sonication may have truly sonic communication functions, too. The angry buzz of a bee trapped under a drinking glass or otherwise being handled may also be sonication and not just wing-buzzing. Cane said the “piping” sound sometimes made by queen bees or by mating bees may also be a form of sonication communication. In short, there are many uses for sonication, and “probably more to be discovered,” Cane said.
Sonication isn’t the same as, say, grabbing a refrigerator and shaking it back and forth like a human would. It’s more like gripping the fridge and then shivering so hard, without any waving of limbs, that the door pops open and all the food falls out. Hard enough that your muscles and skin make an audible buzz.
Indeed, sonication is typically described as a kind of shivering. Bees also shiver more normally to warm up, like humans do, and the biomechanics are nearly identical, though warm-up shivering is often inaudible, conducted at a much lower rate of something like 40 hertz.4 (I find this especially interesting in light of the generally accepted theory that insect wings originated as thermoregulation devices—which they remain in many species. Shivering and sonication are both conducted with muscles that are part of the flight system. And bumblebees are known for excelling at regulating their body temperature.) It’s interesting to note that many flies produce a buzzing sound while conducting warm-up shivering, though they don’t seem to use sonication as a tool as bees do (with the possible exception of using it as an “I’m angry!” signal to predators).
The muscles involved are fibrillar, meaning they are constructed in such a way that their own stretching can spontaneously trigger their own contraction, setting up an ongoing oscillation, or shiver. (Heart muscle is another example of fibrillar action.) Obviously, this is useful in flight as well, turning the bees’ wings into a blur of constant oscillation.
But the flight musculature of bees is indirect. The wings are actually moved by a deformation of the exoskeleton of the thorax produced by the flight muscles. Bees can actually reposition their muscles—the third axillary, specifically—to detach them from the arrangement that produces wing movement. That leaves them with all the vibration and none of the movement, producing a higher-frequency vibration than the drag-inducing wings would normally allow. (The thorax still deforms, but not as much nor in the same way.) Call it the non-flight of the bumblebee.
In all bees, this allows shivering. In sonicators, an even faster vibration, transmitted through their legs and mandibles, or just through the air, turns into a tool. (Presumably, this muscle action is always part of the normal buzz of a flying bee, along with the sound of the wings, though it appears no one has isolated all of the component sounds.) It’s unclear why honeybees don’t go beyond shivering and into sonication.
Bees are already legendary for their array of astonishing abilities—flight, honey-making, venom-injection, hexagonal chambered hives, freakishly complex and alien social systems, dance-based languages, and so on. And here’s yet another ability all the more astounding for not being added to the list in textbooks everywhere. Bees can whack stuff with self-created sonic blasts! I mean, come on! Even the famous “Dungeons & Dragons” adventure game, which has whole sourcebooks devoted solely to categorizing the exotic, menacing abilities of beasts, gives its giant bees only swarming and venom as special dangers.
I must say, however, that it’s very pleasing to have heard the other buzz before I heard about it. Given a tomato garden or the like, anyone can. “It’s like bird song,” Cane said. “It’s available to the public without lots of equipment or expensive supplies.”
Indeed. Especially without your iPods and ATVs. As for me, I’m feeling Cheshire-catty and richly rewarded by the beauty and mystery so freely offered by the natural world. When something as commonplace as a bee on a flower can turn into something so utterly gobsmacking, I can only smile at the thought of what awaits under the next leaf, around the next tree, at the edge of the next pond.
1 “Why Is That Bee Giving Me a
Raspberry?” at http://gears.tucson.ars.ag.gov/ic/buzzpol/buzzpol.html.
2 “Activity
of Asynchronous Flight Muscle from Two Bee Families During Sonication
(Buzzing)” by Marcus J. King, Stephen L. Buchmann and
3 “Bumble Bee-Initiated
Vibration Release Mechanism of Rhododendron Pollen” by Marcus J. King and
Stephen L. Buchmann, “American Journal of Botany,”
vol. 82 no. 11, 1407-1411 (1995), available at http://links.jstor.org/sici?sici=0002-9122(199511)82:11%3C1407:BBVRMO%3E2.0.CO;2-5.
4 “The Hot-Blooded Insects: Strategies and Mechanisms of Thermoregulation” by Bernd Heinrich.
Significant sources not cited in the text or footnotes
include: Prof. (emeritus) Charles Michener (the world’s top bee expert),
University of Kansas, via e-mail; Prof. Robert Minckley,
University of Rochester, via e-mail; “Monster Manual” by Monte Cook, Jonathan
Tweet and Skip Williams; Prof. Gard Otis, University
of Guelph, via e-mail; Prof. Marla Spivak, University of Minnesota, via e-mail; Prof. Kirk Visscher, University of California, Riverside, via e-mail;
Prof. Mark Winston, Simon Fraser University, via e-mail; www.bumblebee.org/foraging.htm
(anecdote about angry sonication). Jim Cane phone
interview conducted April 24, 2006. Stephen Buchmann,
president of The Bee
Works, professor at the University of Arizona and research
entomologist at US Department of Agriculture-Agricultural Research Service Carl
Hayden Bee Research Center, Tucson, Arizona; and Laurence Packer, interviewed
via e-mail. Thanks to Prof. Michael Breed,