60-Second Science

Insects Invented Gears Long before Humans Did

Planthopper nymph hind legs meet under the belly in plates fringed with interlocking teeth that function like mechanical gears, to ensure a straight jump. Wayt Gibbs reports

Planthoppers are tiny insects, only a couple of millimeters long. But man can they jump. An adult planthopper can sweep its two hindlegs together to spring forward more than a meter—the equivalent of you or I leaping over tall buildings in a single bound.

But these superjumpers must push off with both legs at almost exactly the same time, or else they’ll go into a spin and wipe out.

A new study reports that the planthopper Issus coleoptratus evolved a foolproof solution to this problem: in young nymphs of the species, the two legs meet under the belly in plates fringed with interlocking teeth. They function just like mechanical gears. The work appears in the journal Science. [Malcolm Burrows and Gregory Sutton, Interacting Gears Synchronize Propulsive Leg Movements in a Jumping Insect]

As the bug cocks its two hindlegs forward and then thrusts them back to push off, those gears guarantee that both limbs complete their motions within 30 millionths of a second of each other. [Video]

The synchronized forces propel the nymph straight through the air at up to nine miles an hour—impressive. But adult planthoppers can jump at more than 12 miles an hour. And they do it using smooth-rimmed hips, with only friction to keep their legs in sync.

So perhaps the gears are like training wheels, just there until the youngsters learn how to jump straight.

—Wayt Gibbs

[The above text is a transcript of this podcast.]  

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