A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Is it aerodynamically impossible for bumblebees to fly?

May 4, 1990

Dear Cecil:

When I was in college, not so many eons ago, it was pretty much an article of faith among us intellectual iconoclasts that, though we could put a man on the moon, we still had no idea how a bumblebee could fly. Do we?

Cecil replies:

Of course. You think this is on a par with quantum mechanics? The basic principles of bumblebee flight, and insect flight generally, have been pretty well understood for many years. Somehow, though, the idea that bees "violate aerodynamic theory" got embedded in folklore.

According to an account at http://www.physics.org/featuredetail.asp?id=32, the story was initially circulated in German technical universities in the 1930s. Supposedly during dinner a biologist asked an aerodynamics expert about insect flight. The aerodynamicist did a few calculations and found that, according to the accepted theory of the day, bumblebees didn't generate enough lift to fly. The biologist, delighted to have a chance to show up those arrogant SOBs in the hard sciences, promptly spread the story far and wide.

Once he sobered up, however, the aerodynamicist surely realized what the problem was — a faulty analogy between bees and conventional fixed-wing aircraft. Bees' wings are small relative to their bodies. If an airplane were built the same way, it'd never get off the ground. But bees aren't like airplanes, they're like helicopters. Their wings work on the same principle as helicopter blades — to be precise, "reverse-pitch semirotary helicopter blades," to quote one authority. A moving airfoil, whether it's a helicopter blade or a bee wing, generates a lot more lift than a stationary one.

The real challenge with bees wasn't figuring out the aerodynamics but the mechanics: specifically, how bees can move their wings so fast — roughly 200 beats per second, which is 10 or 20 times the firing rate of the nervous system. The trick apparently is that the bee's wing muscles (thorax muscles, actually) don't expand and contract so much as vibrate, like a rubber band. A nerve impulse comes along and twangs the muscle, much as you might pluck a guitar string, and it vibrates the wing up and down a few times until the next impulse comes along. Cecil is sliding over a few subtleties here, but nobody ever said science for the masses was pretty.

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