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October 10, 2013

Art imitates life: A bug with a gearbox


Below, an article from The Economist about the discovery.


Meshing together rotating gears, such as in a car's gearbox, has long been thought of as a man-made solution to transmitting motion. But rather than a machine being the first to use gears, it seems nature got there earlier. This week young members of a genus of stocky little insects called Issus were shown to use gearing in their legs to hop around plants.

This is believed to be the first observation of mechanical gearing in a biological structure. The discovery was made by a team led by Malcolm Burrows of the University of Cambridge using a combination of anatomical analysis and high-speed video. Their findings, reported in Science, show that the gears in the hind legs of an Issus, which are commonly found hopping around European gardens, have a remarkable similarity to those used in cars and bicycles (below).


More intriguingly, the gear teeth have rounded corners at the point they mesh—a feature that engineers use in man-made gears as a shock-absorbing function to prevent the gears' teeth from breaking off. The insects' gears are used on their opposing hind legs to lock them together and synchronise movement during powerful jumps (below).


Without the precision provided by the gears an Issus would spin out of control. The degree of co-ordination would be impossible to achieve with a nervous system alone because the neural impulses would be too slow, says Dr Burrows.

The gears, though, are found only in the insects' juvenile, or nymph, stages, when they cast off rigid skin as they grow. Why the gears disappear by adulthood is not known, but the researchers suspect that it may be similar to a problem that every carmaker faces: if one tooth in the gearbox breaks the whole mechanism is impaired. Perhaps the juvenile Issus can repair a broken gear tooth in one of its regenerative stages, but it would be unable to do that as an adult. Another explanation could be that larger adults develop the equivalent of a bigger thigh bone that provides the power for co-ordinated leaps.

Cog-like structures are found in other animals, but their role has been seen as ornamental rather than functional. Now that mechanical gears have been found in one creature, scientists — and engineers — will look harder to see if they exist in others.


Below, the abstract of the report in Science alluded to in the story above.


Gears are found rarely in animals and have never been reported to intermesh and rotate functionally like mechanical gears. We now demonstrate functional gears in the ballistic jumping movements of the flightless planthopper insect Issus. The nymphs, but not adults, have a row of cuticular gear (cog) teeth around the curved medial surfaces of their two hindleg trochantera. The gear teeth on one trochanter engaged with and sequentially moved past those on the other trochanter during the preparatory cocking and the propulsive phases of jumping. Close registration between the gears ensured that both hindlegs moved at the same angular velocities to propel the body without yaw rotation. At the final molt to adulthood, this synchronization mechanism is jettisoned.

October 10, 2013 at 12:01 PM | Permalink


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Cogs, yes. Gears? They more closely resemble (to me) an even later human development - the zipper. Which holds things together.

Posted by: John A | Oct 11, 2013 7:28:04 PM

I find this mind boggling,

although I often think (just think about what I'm going to say)

there are gears misaligned in my head (you too, huh?).

Posted by: Joe Peach | Oct 10, 2013 6:20:42 PM

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