Saad Bhamla: One insect's pee appears to defy physics Professor Saad Bhamla believes all science puzzles are important, even silly ones. His research into the glass-winged sharpshooter's "butt flicker" led to a discovery about the physics of insect pee.

How do insects pee? A seemingly silly question that led to a physics discovery

  • Download
  • <iframe src="https://www.npr.org/player/embed/1187250226/1187665102" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript

MANOUSH ZOMORODI, HOST:

It's the TED Radio Hour from NPR. I'm Manoush Zomorodi. And on the show today, Animal Enigmas - the quest to solve some of today's biological mysteries, including how insects pee.

SAAD BHAMLA: I have a beautiful backyard. You know, we could finally have, like, a nice house with a backyard for the kids and the dogs to play. And of course, the Southeast, because of its nice weather, has so many, so many different types of bugs basically all year around.

ZOMORODI: Saad Bhamla is a professor at Georgia Tech, and he researches all kinds of insects, including those in his backyard.

(SOUNDBITE OF WATER FLOWING)

BHAMLA: We have an old water fountain feature, and every day as I walk out, my 3-year-old son and I will kind of peek into it. We'll see tiny flies that are both flying in the air, but then they land on the water surface and skim and glide. We walk amongst the grass and see lots and lots of tiny insects that are hopping. And now it's spring, so we'll observe these carpenter bees.

(SOUNDBITE OF CARPENTER BEES BURROWING)

BHAMLA: And you can see these fine shavings of wood as these bees are digging in. I don't know. It just goes on and on.

ZOMORODI: We should point out Saad is not your typical bug and animal researcher.

BHAMLA: Yeah. I'm trained as a chemical engineer on paper. All my degrees are in chemical engineering. I didn't even know I love bugs till my young adult life, and I slowly started to look at them through this lens of physics and mathematics and engineering. I just realized there are so many puzzles.

ZOMORODI: You see - it sounds like you see the world very differently than most of us, who would be worried about finding a tick between our toes or swatting at mosquitoes. It's a wonderland. It's a lab for you just waiting for experimentation.

BHAMLA: Just what you said. I feel so lucky because I had, like, wool in front of my eyes. And one day, it struck me that the entire world is your lab. Like, the Amazon rainforest is your lab. The backyard is a lab. That's where science happens. And all you need is this perspective, and it changes everything. And you can do science 24/7.

ZOMORODI: Saad Bhamla continues from the TED stage.

(SOUNDBITE OF TED TALK)

BHAMLA: I love bugs. I think of them as nature's tiny engineers because they come up with the most extraordinary and incredible solutions to life's problems. And I just love observing them because they're so full of surprises and curiosities. Today, I'm going to tell you a story about one of nature's most extraordinary engineers that pushes the limits of fluid mechanics and bioengineering and arguably solves their No. 1 problem - how insects pee. Sit back and relax. You're in for a treat.

A few years ago, my student Elio Challita and I observed this tiny insect having a private moment in our own backyards in Atlanta, and we couldn't believe our eyes. This insect was peeing for hours, and we were blown away. We had never seen anything like this. So I observed this bug and it was, you know, flicking droplets very fast, so you could hardly see it, but you could feel it on your hands, and it would make you kind of question yourself whether it was just raining under a tree, if that makes sense.

ZOMORODI: So you were standing there in your yard looking at a tree, and you could see - like, even though it was really quick and really small, you could see it flicking something.

BHAMLA: Right, because we all carry a beautiful scientific instrument in our pocket. So I just had pulled up my iPhone.

ZOMORODI: Oh.

BHAMLA: And you can do two great things. I can buy a $5 magnifying lens and put it in front of my camera, and so now you've got, essentially, a pretty decent microscope, especially for bugs. And the second feature is you can switch to slow motion. And this is remarkable, right? So I recorded a video, and I was like, hey, there's something happening. There's a droplet at its butt, and it's flicking it. And, you know, I was like, all right. Challenge accepted, bug.

ZOMORODI: Saad needed to figure out how the insect peed.

BHAMLA: Right. So this was a glassy-winged sharpshooter, Homalodisca vitripennis. And these are sap feeders. And it's, you know, a system. You have to think about feeding and excretion. What goes in must come out.

ZOMORODI: Hence the pee, which, of course, plenty of insects do.

BHAMLA: Lots of insects, and they do it in so many different forms, and they do it on the fly. They do it while sitting.

ZOMORODI: And most of them pee more or less like us - you know, in streams.

BHAMLA: Yeah. It's amazing.

ZOMORODI: But the glassy-winged sharpshooter is the only one that flings little pee missiles, and Saad had a hunch that complex physics were involved. So he and his student, Elio, brought these sharpshooters into the lab.

BHAMLA: So we take our high-speed cameras and we measure them. And then I tell Elio, just ask a simple question, is how fast are these droplets moving?

(SOUNDBITE OF TED TALK)

BHAMLA: We realize that this insect forms a droplet of pee, and then it flings them at extreme accelerations of 40 G-forces. That's 40 times faster than the sprint of a cheetah. These insects are really packing a punch from their butts. And we wanted to take a closer look at this flicker, so we took a look under a microscope at its business end. And this beautiful structure has a scientific name. It's called a butt flicker.

(LAUGHTER)

BHAMLA: And this is what we discovered. We realized that this insect had evolved springs and latches just like a catapult so that it could efficiently hurl its droplets of pee repeatedly at these high accelerations. Now, we wanted to measure the speed at which this flicker was moving and the droplets, so we measured the speed of both the droplets and the flicker. And this is where we made a puzzling observation. The speed of the droplets in air was faster than the flicker. So if you take a ratio of that, we were expecting it to be 100%, but it turns out that the speed of the droplets are about 150- to 200% faster than the flicker itself.

ZOMORODI: Wait, wait, wait, wait. Why didn't it make any sense? What was puzzling you? Like, personally, I would have said, wow, he has a butt flicker, as you call it, on his body. That's amazing enough. But then what was it that made you think like, huh, there is a mystery to be solved here?

BHAMLA: Right. So as a scientist, we're greedy because - the butt flicker was great - OK, so we know something about the anatomy.

ZOMORODI: (Laughter).

BHAMLA: And it's flicking it. OK, that's great. But wouldn't it be amazing if we could unravel much more interesting physics?

ZOMORODI: Ah.

BHAMLA: And so the speed mismatch was bothering us because if a Yankees pitcher throws a baseball, and they'll say, oh, it's going at 100 miles an hour, at some point the pitcher's fingers had to be traveling at 100 miles an hour. Because if I throw a baseball at, say, 30 or 40 miles an hour, and in midair, this baseball is now moving at 100 miles an hour, faster than my fingers or arm, that doesn't make sense because, where does that extra energy come from? And we expect that energy balance to match. Things cannot move faster than the object that propels them.

ZOMORODI: Unless, like, it would - say, has an extra bit of force added.

BHAMLA: Precisely, or some storage of energy somewhere in that process that was unclear to the eye at first glance.

(SOUNDBITE OF TED TALK)

BHAMLA: So to solve this puzzle, we went back and looked at our videos. And we realized that unlike a baseball that's rigid, these tiny droplets are squishy, and we had a aha moment. We were wondering if this insect is storing energy due to the surface tension just before launch. And to test this, we did, naturally, what any of us would do. We converted our kitchen tables into a lab. So now we're going to place droplets on a speaker to squish them at high speeds, and this is what we discovered. We realize that water that flows in our faucets, like, a liquid, at these tiny scales, due to surface tension, with the right timing can get a kick, store energy, and if you time it just right, you can launch these off at extremely high speeds just like a child on a trampoline.

ZOMORODI: OK, so kids on a trampoline, and they're jumping. And if they get their timing just so, they can catch a bigger bounce. And so with your analogy, the butt flicker is like a trampoline, and the kid is like the droplet of pee getting a turbocharge.

BHAMLA: Right. And so the droplets were actually acting like a liquid spring. And so maximizing this can allow us to really fly far off.

ZOMORODI: So explain how that's happening here, Saad. I think you need to walk us through the butt flick, as it were.

BHAMLA: Sure. So the droplet is rested and cradled in this gorgeous butt flicker. It's about 100 microns in diameter. It's the most beautiful pee you've seen, right? It's this gorgeous drop, perfectly spherical. And then it cocks its butt flicker because it's got this tiny, resilient spring, and like a catapult, maybe by 10 or 15 degrees more it'll cock it. And then it starts to rotate, and as it rotates, you can observe the droplet squish because of surface tension. And the flicker will reach the end of its trajectory, and then the droplet takes off just like a tiny, tiny, spherical elastic rocket. And this whole thing happens in 100 milliseconds.

ZOMORODI: Oh, wow.

BHAMLA: Your blink of an eye is, like, maybe 200 milliseconds. So it's, you know, faster than the blink of an eye. The fact that it's doing all of this is baffling.

ZOMORODI: Yeah. But you solved the mystery. I guess the question is, though, what does this tell you about the evolution of this bug?

BHAMLA: That nature has had far more time to tinker than us. Oh, goodness. But there are two reasons. So these are xylem sap feeders. You know, that's what this particular sharpshooter feeds on. And xylem is just 95% water. It just has a few minerals. So they have to glug, you know, 300 times their body weight.

ZOMORODI: Oh.

BHAMLA: So the reason they are drinking so much is because they need energy, right?

ZOMORODI: Yeah.

BHAMLA: But they have to come up with an energy-efficient way to excrete this. And if they made jets, it would be 4 to 8 times more expensive energetically.

ZOMORODI: Oh.

BHAMLA: And because they're living on this frugal diet, every part of their energy extraction ways is trying to minimize how much energy they waste.

(SOUNDBITE OF TED TALK)

BHAMLA: These things are tiny. They're smaller than my pinky. In fact, surface tension that enables them to store energy in these droplets to launch is actually an impediment because gravity doesn't matter, and surface tension sticks these droplets to their bodies. So they actually have to flick these droplets away. It's actually very difficult for these tiny bugs to pee. And that's why I just love studying bugs. This tiny engineer has figured out to survive on barely just water through the xylem fluid, and it's figured out, to do so, it has to drink a lot and pee a lot. In that sense, it's not so different from other engineers I know on a Friday night at a bar...

(LAUGHTER)

BHAMLA: ...But to do so, it's figured out it has to evolve this catapulting structure and fling these droplets at high speeds.

ZOMORODI: I'm just trying to get in the head of the listener here, Saad, but there will be people who think - that's so great, Saad. Thank you so much for this illumination of how these bugs pee, but really, in the grand scheme of things, why should we care?

BHAMLA: Yeah. Why should we care? So this is how I live my life, and maybe I'll change it in the future. But I have two halves to my life. And one is all about organisms, and the other half I actually put on my engineer's hat, and we build $1 hearing aids. We built a 20-cent paper centrifuge for malaria diagnostics. We've just spun out a company using barbecue lighters for mRNA vaccine delivery to make it accessible to 4 billion people who still don't have access to it. And that's the engineering part. I love it, too, right? I think it's important, and I use taxpayer money and try to do good. And we train students how to do frugal science. But there is a joy in the other half where we just study bugs, and the application there is it just makes - it's the joy of discovering things. The application is making other people be able to appreciate nature. You know, holy smokes, you can look at insects and study fluid dynamics. To me, that - we need more of that. That's a good enough application for me because if you solve a puzzle, it's just such a great advance for humanity.

ZOMORODI: That's Saad Bhamla. He's an assistant professor of biomolecular engineering at the Georgia Institute of Technology. His student, Elio Challita, just officially got his PhD on the sharpshooter. To watch Saad's full talk, go to ted.com.

Copyright © 2023 NPR. All rights reserved. Visit our website terms of use and permissions pages at www.npr.org for further information.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.