Water lily beetles "ski" across the surface of a pond at a speed of up to 0.5 meters per second. This, researchers say, would be equivalent to a human travelling at about 311 mph.
Using high-speed cameras, bioengineers from Stanford University filmed the insects' as they skittered over plates filled with water. Slowing the video down revealed how they use their wings to skim across the water's surface like tiny skiers.
Measuring a mere 0.2 inches in length, water lily beetles ("Galerucella nymphaeae") live in ponds, streams and lakes across North America, spending most of their time fluttering from lily pad to lily pad.
"The surface tension forces are so large compared to this little thing, but it has the capacity to fly at half a meter per second on the surface of water without ever detaching from the water's surface," said study co-author Manu Prakash, an assistant professor with the Department of Engineering at Stanford University, in a news release. "It's one of the fastest-known locomotion strategies on the surface of water."
When settling on the water, a water lily beetle lifts each leg, one at a time, and carefully places them back so that only the tip comes into contact with the water's surface. Researchers say maintaining contact with the water is key to the beetle's ability to travel from lily pad to lily pad.
When preparing for take off, a beetle raises its two middle legs, unfurls its wings, and flaps in a figure-eight motion. As the wing-beat action settles into a stable frequency of about 115 cycles per second, the insect rocks slightly, builds momentum and shoots across the water without ever losing contact with the surface.
Since the beetles are moving so swiftly, they actually interact with the ripples generated by their own motion, but grip the water with their claws just enough to remain steady through what is likely a bumpy ride.
"This makes the insect feel as though it is on a pogo stick on the water," said Haripriya Mukundarajan, a mechanical engineering graduate student in Prakash's lab.
Even though skimming across the water requires more energy than flying in the air, due to the drag, water lily beetles rarely take to the skies - generally only when threatened by predators. Researchers believe the insects move on water rather than air because they feed on water lily leaves floating on ponds.
"The beetles look so beautiful on film, and this project is so rich with opportunity to do really fascinating research in so many fields, including fluid mechanics, biomechanics and non-linear dynamics, and synthesize them into an explanation of this biological phenomenon," Mukundarajan added.
"Their findings were recently published in the Journal of Experimental Biology.
