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WATER BUGS DO IT, BUT CAN WE?

GERRIDS ARE a family of insects including water bugs, pond skaters, water striders and jesus bugs, all of which can travel atop the water. Water bugs use their mass, musculature and balance to make use of the liquid’s surface tension. Recently, researchers have devised a robot that mimics the gerrid’s aquatic talents.

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Science, the weekly magazine of the American Association for the Advancement of Science, July 31, 2015, has two articles on this robotic advance. “Jumping on Water: Surface-tension-dominated Jumping of Water Striders and Robotic Insects” reports on research performed by Je-Sung Koh and colleagues at Seoul National University, Harvard and the Polish Academy of Science. “Two Leaps Forward for Robot Locomotion,” by Dominic Vella, is a summary of their research. Abstracts are available at Jumping on Water and Two Leaps, respectively.

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A water strider, Aquarius remiges, travels atop the water by exploiting surface tension—in a precise manner. Image from Science, July 31, 2015, by Dennis Drenner/Visuals Unlimited/Corbis.

Water molecules attract each other, causing a thin film at its surface. This surface tension can support something, provided it distributes its miniscule weight over a large surface area.

Gerrids have low body mass and six long slender legs evolved to exploit this. The front two are shortest and used to capture prey. The middle ones, of intermediate length, have locomotion duties. The rear two legs steer and distribute the insect’s weight in an optimal manner.

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At left, water strider preserves surface tension to jump. At right, surface penetration. Image from Science, July 31, 2015.

Koh and his colleagues identified that water striders propel themselves by rotating the curved tips of their legs inward and downward—with a force just below that of piercing the water’s surface film. Amazingly enough, the legs’ action produces minute waves off of which they push, generating forward thrust. A water strider can move faster than a meter/second.

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A water strider’s jump seen in high-speed photography. Image from Science, July 31, 2015.

The insect’s body and legs are hydrophobic, water-repelling, by means of microscopic hairs, thousands of them per sq. in. Should the insect become submerged, these tiny hairs trap air. They also increase the surface area of its leg tips.

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The water strider robot fabricated by Koh and his colleagues. Image from Science, July 31, 2015, by Biorobotics Limited/Seoul National University.

Like a real water strider, the robotic one can jump as well as stride. Researchers modeled its triggered-hinge mechanism after a flea’s musculature. They used a MEMS (MicroElectroMechanicalSystem) process to fabricate a “full-size” robotic water strider just 2 cm. (0.8 in.) in length and weighing 68 milligrams, about 0.002 oz.

By studying varied triggering forces for the robotic legs, Koh and his colleagues were able to quantify the physics of water strider locomotion. They conclude, “The experimental results improve our understanding of the dynamic interaction between an unconstrained free body and a liquid surface, as observed in semi-aquatic arthropods in nature.” ds

© Dennis Simanaitis, SimanaitisSays.com, 2015

One comment on “WATER BUGS DO IT, BUT CAN WE?

  1. Anton Thortzen
    November 23, 2015

    No, apparently we can’t, but wouldn’t it be wonderful if we could? Almost as desirable as if we could fly like birds. Nature is amazing, but smartly designed robots are too. One wonders where it will take us in the future. A nano-robot finding cancer cells in our body and destroy them? Jesus bugs!!! – what an apt name!

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