How Pygmy Mole Crickets Jump on Water

The pygmy mole cricket. CREDIT: Malcolm Burrows et al View full size image

Researcher Malcolm Burrows was sitting next to a South African pond eating lunch one day when he heard an odd noise coming from the water. What he found surprised him: pygmy mole crickets hopping off the surface of the water onto the bank.

Although pygmy mole crickets were known to perform this trick, nobody had figured out exactly how it was done. So Burrows, a researcher at the University of Cambridge, took some of the pygmy crickets back to his lab and filmed them in slow-motion to understand how they executed this feat.

He found that the creatures have spring-loaded, oar-like paddles on their back legs that help them jump. Their back legs are 4.5 times longer than their front legs, and their large muscles contain a protein called resilin that is "the perfect elastic," Burrows said in a release from Cell Press, publishers of the journal Current Biology, where Burrows' study will appear tomorrow (Dec. 4).  As those oars penetrate the water, they fan out. The cricket then "grabs" a ball of water, sending it downward as its body soars upward.

"Pygmy mole crickets have solved the most difficult task of jumping from the surface of water," Burrows said in the release. "For small insects, water can be a deadly, sticky trap: Water grabs and holds an insect, offering it as an appetizing snack for an alert fish. Pygmy mole crickets turn the stickiness of water to their advantage and use this property to enable jumping."

The insect oars could guide the design of propellers for tiny robots, Burrows said.

In the animal, the unique legs serve several purposes. "This is an animal that has to do many things with its legs: dig burrows in the ground, jump rapidly to escape predators on land, and get itself out of water before it is eaten or drowns," he said. "It has solved a hugely difficult problem with a multifunctional mechanism that can propel jumps on land and water."

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