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Froghopper Bug Crowned "World's Greatest Leaper"

By John Roach
for National Geographic News
July 30, 2003
 
A sap-sucking bug that coats plants with wads of foamy spit has been crowned the insect world's greatest leaper. It has more jumping prowess than fleas, out hops the springiest grasshoppers, and clears the high bar more quickly than bush crickets.

Philaenus spumarius, commonly known as a froghopper or spittle bug, is a mere 0.2 inches (6 millimeters) long, but employs a novel catapult mechanism to launch itself upwards of 28 inches (70 centimeters) into the air.


"They do jump a heck of a long way," said Malcolm Burrows, a neurobiologist in the zoology department at the University of Cambridge in England.

The bugs are found in woodland edges and grasslands the world over. Developing young create a frothy mass commonly known as cuckoo spit on plants in the early spring and summer to hide from predators such as ants. Adults live in the open and leap when threatened and to go between plants in search of food.

Burrows, whose primary research interest is in how animals use the individual cells in their brains to generate movement, stumbled upon the froghopper's leaping agility while looking for an insect model to clear the next hurdle in his work.

What he found was an insect that accelerates from the ground with a force that is 400 times greater than gravity. For the sake of comparison, we humans jump with a force that is two to three times that of gravity.

"[The froghopper] experiences something like 400 g's," said Burrows, whose research on the froghopper appears in the July 31 issue of the journal Nature. "That's a lot. We pass out when we experience about 5 g's." Merriam-Webster defines g as a unit of force equal to the force exerted by gravity on a body at rest and used to indicate the force to which a body is subjected when accelerated.

William Heitler, a biologist at the University of St. Andrews in England, said the work by Burrows is well done and the results impressive. "I've seen froghoppers in my garden and knew that they could jump well, but I had no idea that they were such absolute champions," he said.

Catapult

The animal kingdom possesses two basic body designs that enable certain creatures to leap away from their predators, launch into flight, or spring from place to place in speedy fashion.

The long legs of animals such as kangaroos and frogs give them levering power that allows them to jump with ease. Short-legged hoppers rely on the release of stored energy in a rapid catapult action, Burrows explains in his paper.

The insect world takes advantage of both designs. Crickets use the leverage provided by their long legs, fleas store energy to power their short legs, and grasshoppers combine features of each. Froghoppers, which have relatively short legs, catapult, said Burrows.

"It has to store energy in advance of being able to jump and what it has is two huge muscles in its body," he said. "It invests 11 percent of its body mass in these two muscles."

These muscles, which power the rear legs, are located in the froghopper's chest. As the insect readies to leap, it tucks up and holds its rear legs in a cocked position on a ridge between one part of a hind leg and another. The rear legs stay locked in this position until the jumping muscles load up with enough energy to break the legs free from the ridge, launching the froghopper into the air, explained Burrows.

"When it has enough force it sort of snaps open and it does this incredibly fast," he said. In less than a millisecond, the leg extends and accelerates the body at speeds up to 13 feet (4 meters) per second.

"The catapult mechanism is exactly what we would expect good jumpers with small legs to use, but this is the most spectacular example that I have heard of so far," said Heitler. "Humans probably learned to use catapults a few thousand years ago, but insects like these evolved catapults inside their own bodies hundreds of millions of years ago."

The process of loading up the jumping muscles takes just about a second and the release that sends the froghopper flying through the air happens in a millisecond. To study this action, Burrows used a high-speed video camera capable of shooting 2,000 frames per second. The insect jump takes up two frames of tape.

While persuading the insects to jump in front of the camera proved difficult, "the hardest part was to catch the little guys in the first place because they jump so well," said Burrows.

The next stage in Burrows' research is to attach wires to individual cells in the froghopper's brain to record how the nervous system controls the simultaneous, rapid action of the insect legs.

"I'm trying to understand how these circuits of nervous cells control movements," he said. Since insects have relatively large brain cells and fewer of them than creatures such as humans, they make for simple research models, added Burrows.

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