The ins and outs of how insects fly

The ins and outs of how insects fly

Photo by Anne Nygård on Unsplash

Originally published 12 July 1999

Sum­mer­time, when the livin’ is buggy.

Mos­qui­toes. Black flies. Yel­low­jack­ets. No-see-ums.

And, of course, the house fly, that dirt-foot­ed sum­mer­time pest, who does par excel­lence exact­ly what its name suggests.

What all these wretched lit­tle ter­rors have in com­mon is the gift of flight. 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 stingers 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. Last win­ter in the Caribbean I saw a “fly­ing fish” that stayed aloft above the waves for what seemed an impos­si­bly long time.

But insects were the first ani­mal to evolve active 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.

The ques­tion is: 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 air­plane-like flight.

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

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

Mount a sta­tion­ary gnat’s wings in a wind tun­nel, as aero­nau­ti­cal engi­neers are wont to do, and the mea­sured forces are sub­stan­tial­ly small­er than those need­ed for stay­ing aloft, much less for flit­ting about. What­ev­er a gnat is, it’s not an airplane.

Lots of the­o­ries have been gen­er­at­ed to explain insect flight, involv­ing upstroke and down­stroke, rapid wing rota­tion and rota­tion rever­sal. 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. Clap and fling is well and good, but, still, no one is quite sure how the crit­ters fly.

Dud­ley’s essay in Nature intro­duced new exper­i­men­tal work on fruit fly flight by biol­o­gists Michael Dick­in­son and San­jay Sane of the Uni­ver­si­ty of Cal­i­for­nia, and Fritz-Olaf Lehmann of the Uni­ver­si­ty of Würzburg am Hub­land in Germany.

Dick­in­son, Sane, and Lehmann built a scale mod­el of fruit fly wings, each wing some­what larg­er than a human hand, with attached mul­ti­ple motors that give them motion about three inde­pen­dent axes. To make them dynam­i­cal­ly equiv­a­lent to the wings of a tiny insect in air, they put the whole appa­ra­tus in a vat of vis­cous oil. At the base of one wing were sen­sors that mea­sured instan­ta­neous forces.

Then they set the appa­ra­tus going — flap­ping and spin­ning, clap­ping and flinging.

Out of all of this the biol­o­gists came up with a the­o­ry of insect flight that focus­es on three mech­a­nisms: delayed stall, rota­tion­al cir­cu­la­tion, and wake cap­ture. Nev­er mind exact­ly what these are; what’s impor­tant here is that we now have a bet­ter exper­i­men­tal notion of how insects fly.

So what? Well, for one thing, we can 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, and wake cap­ture, an inge­nious mechan­ics of flight con­trived by insects before a ptero­dactyl ever thought of glid­ing off a cliff, nev­er mind the Wright Brothers.

Oth­er more prac­ti­cal pos­si­bil­i­ties present them­selves. Aero­nau­ti­cal engi­neers sup­port­ed by the Defense Depart­ment have been giv­ing a lot of atten­tion to build­ing minia­ture fly­ing machines, called microair vehi­cles, small­er than a human hand, which might make use of these new­ly revealed secrets of insect aero­dy­nam­ics. And nano­engi­neers, who think small have envis­aged fly­ing machines so tiny that they can be seen only with a microscope.

If you think sum­mer is bug­gy now, wait a gen­er­a­tion or so until some trou­ble­mak­ing neigh­bor lets loose an aer­i­al arma­da of nanofly­ers — $29.95 a dozen at Wal­mart — mechan­i­cal stingers to dis­rupt your bar­be­cue, unde­terred by bug spray, rub-on creams, or smok­ing citronella.

Share this Musing: