Gunfire. A rocket launch.

Saad Bhamla, an assistant professor at Georgia Tech’s School of Chemical and Biomolecular Engineering and an expert in “extreme biophysics," knows these are the activities that come to mind when he asks: What moves quickly? Primarily things driven by detonation or combustion — events that involve destruction.

But he’s interested in a different sort of speed, so he refines the question: What are fast movements in nature? Here, too, he knows there are obvious answers. For humans, it’s Usain Bolt crossing a finish line. In the animal kingdom, a cheetah’s pursuit or the flight of a falcon.

These are good guesses, Bhamla acknowledged, but they come up short. He has found a much faster activity, by investigating a phenomenon that, he said bashfully, “not a lot of serious engineers and biologist want to explore."

That phenomenon is the way insects pee. He has discovered that certain pesky critters fling their urine far faster than cheetahs run, and he thinks the discovery might illuminate nondestructive solutions for difficult engineering dilemmas.

The starting point was Bhamla’s fascination with the way liquid waste rains down from trees and plants populated by sharpshooters, sap-sucking pests native to the Southeast United States and northeastern Mexico that have also made significant inroads elsewhere. They threaten California’s wine industry and wreak havoc on citrus fruit in Florida by spreading bacteria from infected vegetation.

Studying the way these tiny beasts urinate, Bhamla said, yields important lessons about the dynamics of speed, all the more urgent given the “global challenge of insect decline.”

“First, we need to learn from nature how she does it, before we, as engineers, can build it,” he said.

The seemingly commonplace insects — they are to plants what mosquitoes are to humans, Bhamla explained — push the limits of what we ordinarily expect of biology and physics. The stream from a tree infested with sharpshooters is so vigorous that it can douse passersby. The effect is known as “leafhopper rain," and it has earned the pest the nickname "pissing fly.”


The sharpshooter is a sap-sucking pest native to the Southeastern United States and northeastern Mexico. (Saad Bhamla)

“It’s crazy when you see it,” Bhamla said. “It’s one of those puzzling things you notice, and then you keep thinking about."

He wondered: Why do these tiny insects emit so much liquid, and how do they do it so quickly?

There was no satisfying data on how insects relieved themselves. So as he prepared to move from California, where he completed his PhD in chemical engineering at Stanford, to take up an assistant professor position at Georgia Tech last year, he promised himself, "When I set up my lab, I’m going to figure out this puzzle. It’s bugging me.”

So began a “curiosity-driven exploration,” which Bhamla undertook as the principal investigator for a lab examining “organismic physics, soft matter and frugal science.” Some of his other projects address exploding plants and ballistic spiders.

Bhamla and his colleagues recorded videos of two insect species, the glassy-winged sharpshooter and the blue-green sharpshooter, as they fed on the plant tissue bringing water up from the roots and then sent droplets of the liquid waste flying in the air. Whereas regular cameras record at about 30 frames per second, they shot at thousands of frames per second. Then they went frame-by-frame, calculating how many millimeters the urine moved per millisecond.

What they found was that the ejected droplets of urine achieved peak acceleration of about 200 meters per second squared, or about 20 times the acceleration of Earth’s gravity. That’s also about 20 times the acceleration of a cheetah, Bhamla observed.

The finding, he said, points to “new ways of moving fast, other than just burning fuel."

“As engineers, we should always turn to nature, because nature has had millions of years to evolve,” he said. “It’s an interesting way to think about how an insect might move really fast without using combustion. It’s nondestructive.”

Bhamla and his colleagues laid out their findings in a video submitted last month to the American Physical Society’s Gallery of Fluid Motion, part of the APS Division of Fluid Dynamics annual conference in Atlanta. Next month, they will present their work at the Society for Integrative and Comparative Biology conference in Tampa to share the results with other biologists. In the meantime, they are working on a paper on the findings.

What they aim to document is how the insects achieve this extraordinary speed — a result, they believe, of a “catapulting mechanism." A stylus at the insect’s rear acts as a spring, aided by long flexible hairs that create a slinging effect.

A single sharpshooter, they found, can ingest up to 300 times its body weight per day in fluid, “making them extreme biological pumps.” They consume so much because the fluid they pursue, “for some weird reason,” Bhamla said, is essentially waste fluid, with low amounts of nutrients.

“To make it worth their while, to get any energy, they have to go through so much material to get enough energy to survive,” Bhamla said.

The sharpshooter uses “a series of internal biological pumps and valves,” the video explains, as it “pushes the fluid across its body to derive nutrients. The fluid is then squeezed out in the form of discrete droplets before getting ejected." The stylus and hairs act as a catapult, sending the water droplet — the projectile — into the air.

The effect really is equivalent to urination, Bhamla said.

“The insect is intaking the fluid, and it has to get rid of it,” he said. “It’s like if I had a straw and was constantly drinking to the point that my bladder just couldn’t hold it.”

There is some dispute about the fastest movements in nature, in large part because of different ways of calculating speed, such as acceleration or sustained velocity. But scientists have looked to many possibilities, such as the venom harpoons launched by jellyfish or the deadly strike mechanism of a mantis shrimp. In terms of peak sustained speed, cheetahs might be the fastest.

Urine has not been a focus of speed research. One study, also out of Georgia Tech and published in the prestigious Proceedings of the National Academy of Sciences, discovered in 2014 that animals weighing more than 6.5 pounds all take about the same amount of time to pee. An elephant’s bladder is 3,600 times larger than a cat’s, but it takes both animals about 20 seconds to relieve themselves, the researchers found.

Insect pee, Bhamla acknowledged, is even further afield from what most researchers prioritize.

“It turns out that nobody in their right mind would care about why insects pee and how fast they pee,” he said, with a touch of pride. But there may be important applications, he maintained, not just to engineering questions about speed but also to the spread of disease and other environmental and health impacts.

Still, he added, “curiosity was enough of a reason to do it.”

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