How an insect using its butt to flick pee droplets could keep your smartwatch dry
The glassy-winged sharpshooter is an insect so impressive when it pees it could inspire more efficient designs for water-resistant devices.
Saad Bhamla was in his vegetable garden in Atlanta, Georgia, when he first noticed the feat. The sharpshooter forms neat, round pee droplets that it flicks away with lightning speed. Bhamla, a Georgia Tech assistant professor of biomolecular engineering, whipped out his iPhone to take some slow-motion videos.
“The more I zoomed in, the more I realized that it was doing something interesting,” Bhamla tells The Verge.
“The more I zoomed in, the more I realized that it was doing something interesting”
It turns out the sharpshooter accomplishes something with its urine that hasn’t been documented in a biological system until now — a phenomenon called superpropulsion. How the sharpshooter does this is detailed in a research paper Bhamla and colleagues published this week in the journal Nature Communications. And it might just help humans figure out how to achieve superpropulsion, too — not with piss but with smartwatches and other devices that dry themselves off.
Simply put, superpropulsion allows an elastic object to fly at speeds faster than the thing launching it. Precise timing between the squishy object and its catapult gives the object an energy boost. To understand this phenomenon, think of an Olympic diver, Bhamla explains. A skilled diver might time a jump to get the maximum resonant energy from the springboard.
After taking the videos with his iPhone, Bhamla and his colleagues turned to high-speed cameras and microscopes to take a closer look at the sharpshooter. What they found was an anal stylus, aka a butt flicker, that’s key to the unique way the insect takes care of business. The butt flicker moves backward to make room for incoming pee, which allows it to form a droplet on the insect’s tail end. At the same time, the flicker compresses the droplet, allowing energy to build through surface tension.
Once the droplet is at just the right size and shape, the flicker rotates backward another 15 degrees. Then it flicks the droplet away like a pinball. The butt flicker is incredibly fast, accelerating more than 40Gs, which is 40 times faster than the acceleration of a sprinting cheetah. What’s more amazing is that the pee flies at an even higher speed than the butt flicker — the telltale marker of superpropulsion.
As a plus, the tactic is also energy efficient. After all, the droplet is moving more quickly than the catapult launching it. Sharpshooters actually pee this way to save energy because they piss a lot. Sharpshooters will drink and pee volumes up to 300 times their body weight a day because they have a super low-calorie, nutrient-deficient diet of plant sap. And it has to fling its pee away to keep the droplet from clinging to it like a glob of maple syrup.
What does this have to do with a smartwatch? The Apple Watch’s Water Lock feature, for example, can already squirt water out of the device after swimming. But as far as Bhamla is aware, devices like this don’t yet utilize superpropulsion. If engineers can learn from the sharpshooter, they might be able to design more efficient water-ejection systems for gadgets. That way, you can keep your watch dry and charged for longer, too. The same kind of technology might be used in hearing aids or anything else you want to make water-resistant.
Bhamla and his team tested out the sharpshooter’s tactics by bouncing water off speakers on their kitchen tables. They used the speakers’ vibration to compress tiny droplets, building surface tension. With precise timing, they could then launch the droplets at high speeds.
While it sounds apt, this useful trick isn’t what earned the insect the moniker “sharpshooter.” It’s mostly known in the US as a pest to farmers. Its bite marks can look like little bullet holes in leaves, and it can transmit disease from one plant to another. Its copious pissing can also whitewash fruits.
Bhamla hopes his research can inspire more people to look at insects with new perspectives. “I think it will just make kids young at heart and in age go in their backyards and look and enjoy,” he tells The Verge. “It’s a lot of fun. That’s good enough for me.”