Wednesday, January 21, 2009

Clap and fling

One A. M. The insidious song. The fateful buzzing at the ear.

Consider, if you wish, this beautiful prize-winning photograph of an Anopheles mosquito in flight after a blood meal, by Hugh Sturrock of the University of Edinburgh. It appeared the 21 December, 2006, issue of Nature.

But don't talk to me about beauty at one A. M. My thoughts are on murder. On turning that little winged bag of my blood into smush.

There's no escape. From wherever they are, they know where we are, and as quick at you can say "aeronautical perfection" they have sunk their proboscis into our flesh.

Birds fly, too, of course. And bats, those furry mammals. Pterodactyls, extinct winged reptiles, were aviators, or at least they knew how to do a terrific glide. Certain fish put on a good imitation of winged flight. Sometimes we'll see a "flying fish" here in front of the house that stays aloft for what seems an impossibly long time.

But insects were the first animal to evolve true flight, and they're still champs when it comes to maneuverability. They can take off backwards, fly sideways, land upside down, and make love on the wing. And suck our blood, all the while making their merry music.

How do they do it?

For birds and bats the answer is fairly straight forward. The physics of airplanes more or less applies. A wing with an aerodynamic shape is cocked into the wind. A single vortex of air flowing around the wing generates lift. And if the wing is flapping, well, then this more complex behavior can be broken down into consecutive instances of airplanelike flight.

In other words, any aeronautical engineer can pretty much tell you how birds and bats fly.

But things get rather more complicated with insects, especially the tiny ones. The viscosity of air becomes a problem. The biologist Robert Dudley says it's like trying to swim in molasses. Can you imagine a human swimmer in molasses having the agility of a mosquito?

Lots of theories have been generated to explain insect flight, involving upstroke and downstroke, rapid wing rotation and rotation reversal. Some scientists talk of something called "clap and fling," where the wings come together on the upstroke in a way that helps generate lift on the downstroke. Other talk about "delayed stall," "rotational circulation," and "wake capture."

I suppose we could take a certain philosophical delight in the complexities of insect flight while we are laying awake at night with that mosquito buzzing near our ear. The buzz is the audible physics of delayed stall, rotational circulation, wake capture, and maybe some clap and fling. A marvel of evolution. perfected long before a pterodactyl ever thought of gliding off a cliff, never mind the Wright Brothers.

Ingenious! Just look at that lovely photo again.