Gearing up to jump: insect leg cogs

A species of insect that employs gears on its back legs to coordinate its leaping movements has been described by Cambridge scientists...

Using high-speed camera footage running at over 7000 frames per second, zoologist Malcolm Burrows and Gregory Sutton captured the launch movements of the planthopper Issus coleoptratus, a small insect that can take off at over 20 kilometres per hour and can leap over a metre in a single jump.

The insects propel themselves using their powerful hind legs which, the footage revealed, move within 30 millionths of a second of each other.

To achieve this remarkable synchrony, without which the insect would end up hurtling off sidewards, the researchers have found that juvenile planthoppers employ a rack of 12 gear teeth, measuring about a third of a millimetre long in total, that engage between the two legs as the insect primes itself and then executes a jump.

The teeth whizz past each other at the rate of 50,000 teeth-widths per second, and by doing so the rates of acceleration of the two propelling legs are coupled together so they have to move within millionths of a second of each other, keeping the jump on target.

If the gears become damaged they can be replaced when the insect moults as it grows up, the duo speculate. This might also explain why the adult insects jettison this adaptation and resort to some other mechanism to coordinate their leg movements, since with no ability to shed their skin the ability to repair their gearbox would be limited.

Publishing their findings of the first evidence for a natural gearbox in the journal Science, the two researchers emphasise that their results "demonstrate that mechanisms previously thought only to be used in manmade machines have evolved in nature..."