Why The Leafhopper Doesn’t Break Its Leg On Takeoff


With a name like the green leafhopper, you know that Cicadella viridis is probably going to be a keen jumper. These insects can hop with an acceleration of 152 meters per second squared — many times the acceleration of gravity, allowing a successful takeoff — and an average velocity of 0.88 meters per second. That’s only about 2 miles per hour, but it’s not a bad speed for a creature that’s just a fraction of an inch in size.

Roboticists like to study animals such as these to get ideas on how to create better robots, taking shortcuts by harnessing the “design” power of millions of years of evolution. And so researchers led by the BioRobotics Institute in Pontedera, Italy, turned to the green leafhopper to understand how the insect can jump so fast without breaking a leg or destroying the leaf from which it takes flight. Their study appears in the Journal of Experimental Biology.

The scientists collected 67 leafhoppers, a European native, from cane thickets near Pontedera. Then they filmed the insects jumping in the lab, capturing them on film at a rate of 8,000 frames per second to catch the movements in detail.

The powerful jumps are powered by muscles, but muscle-power alone doesn’t explain what’s going on. The leafhopper’s acceleration is nearly constant, which requires that the insect’s leg exert a constant force against the substrate from which it’s taking off. Muscles can’t provide that constant force, and they work too slow for a takeoff that lasts just a few milliseconds. The muscular force also reaches a high enough level that, on its own, it should break the insect’s delicate leg or punch through a thin surface like a leaf.

To translate that strong variable force from its muscles, the researchers found, the leafhopper moves its legs in such a way that the force becomes constant and the stress on both the insect and its substrate never reaches a point where it becomes damaging. That allows a successful takeoff, letting the insect avoid becoming a meal for something bigger.

Image courtesy of Hectonichus on Wikimedia Commons

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