These beetles use surface tension to water-ski

waterlily beetle

Waterlily beetles (Galerucella nymphaeae) water-ski at up to 0.5 meters per second. That’s equivalent to a human moving at 500 kilometers per hour. 

Manu Prakash and Haripriya Mukundarajan

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Waterlily beetles (Galerucella nymphaeae) literally fly across water, high speed videography and a bit of mathematical modeling reveals.

The beetles have a combination of hydrophobic hairs that line their legs and hydrophilic claws that grip the surface of water without getting too wet. Prior to “take off,” the insects lift their middle pair of legs. Then, the insects beat their wings extremely fast and fly horizontally across a pool of water. It looks a lot like water-skiing.

In lab tests, waterlily beetles reached 0.5 meters per second — without an active brake system. Surface tension keeps the insects afloat, they found. The insects create ripples in the water, which generates drag at speeds greater than 0.23 meters per second (more drag than when the beetles just fly through air). Thus, for these beetles, skiing across a pond at breakneck speeds costs a lot of energy and requires greater wing thrust than normal flying. However, this mode of getting around could be more advantageous for foraging and  help them avoid underwater predators like fish, the researchers speculate March 2 in the Journal of Experimental Biology.

SPLISH SPLASH  Watch a waterlily beetle fly or “ski” across a water surface in the lab. Manu Prakash and Haripriya Mukundarajan<

Helen Thompson is the multimedia editor. She has undergraduate degrees in biology and English from Trinity University and a master’s degree in science writing from Johns Hopkins University.

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