Transcript of The fascinating physics of insect pee | Saad Bhamla (re-release)

They might give you a few chills, but they're also full of weird, wonderful discoveries that remind us just how fascinating our world is. Happy listening. You're listening to TED Talks Daily, where we bring you new ideas to spark your curiosity every day. I'm your host, Elise Hu. Today, scientist Saad Bhamla dives into his research about insects, but not just insects broadly. In his 2021 talk from TED Monterey, Bhamla shares the discoveries about one particular insect behavior he hadn't previously seen, and I hadn't previously thought about until hearing this very talk.

After a short break.

But 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 number one problem: how insects pee. A few years ago, my student Elio Chilita 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 it was so quick we could barely see it, and we were blown away. We had never seen anything like this. We had never seen an insect pee. So today, I'm going to tell you how insects pee, why they pee so much and in this way, and finally, why you should care about insect pee. So sit back and relax. You're in for a treat. So one of the first things we had to discuss is, wait a second, insects pee?

And it turns out that almost all insects pee in one form or the other. It's a closed system. What goes in must come out. But the protagonist of today's story, Homo ladisca, a bit of penis or a glossy winged sharpshooter, and this insect specializes in feeding on xylem fluid from plants. It's a sap sucker, but I think of it as a plant's mosquito. And just after a mosquito sucks your blood, it leaves behind a parting gift. So do these sharpshooters that spread bacteria into these plants, and it causes devastating and deadly diseases in plants, killing them.

This is a huge problem in agriculture, including here in California, where they cause millions of dollars in damage to vineyards. 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. We wanted to take a closer look at this flicker, so we put this insect and took a look under a microscope at its busiest end, and this beautiful structure has a scientific name.

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 percentage faster than the flicker itself. And this is why this is counterintuitive. Imagine a Yankees baseball player throwing a ball at 100 miles an hour. At some point during that throw, their hands and fingers are moving at 100 miles an hour. Say an amateur ballplayer throws a ball at 50 miles an hour, and if you measured the speed of the ball and it's 100 miles an hour in midair, we'd be surprised.

Where would that extra speed come from, right? This is exactly what these insects are doing. So to solve this puzzle, we went back and looked at our videos. We realized that unlike a baseball that's rigid, these droplets, due to surface tension, these tiny droplets are squishy. And we had an aha moment. We were wondering if this insect is storing energy to do 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 to test this. So now we're going to place droplets on a speaker to squish them at high speeds, and this is what we discovered.

We realized 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. And to test this idea of timing, we even built a catapult, or should I say a catapi, and it reinforced this idea to slow the droplets don't go off, and then if you move at the right speed, you flung this.

So I've told you today how these insects use this catapulting structure to store energy in surface tension and throw these droplets at record-breaking speeds to be really number one at number one. But why have these insects evolved this remarkable ability? And there are two reasons for this. Number one is they're on a zero-calorie diet. These tiny bugs are feeding from the xylem fluid that comes up through the roots, through the soil, and goes to the rest of the plants. It's very, very poor in nutrients.

It's just water and some minerals. This is unlike the phloem fluid, which is rich in sugar, coming through photosynthesis at the leaves and going to the rest of the plants. This is akin to a human purely sustaining themselves on a diet of diet lemonade. Very low energy source. You'd have to constantly drink, but you'd have to constantly pee as well. This still doesn't explain why these insects pee in droplets and not in jets, like you and I would if you were to take a bio break. Let's take a look at cicadas.

These are the cousins of these sharpshooters. They're also xylem fluid feeders, and they pee in jets. And the second reason for why these insects pee in droplets is size. 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 a 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. But to do so, it's figured out this. It has to evolve this catapulting structure and fling these droplets at high speeds.

And that's why I always tell my students when we explore new bugs, it's not a bug. It's a feature. OK, so why should you care about insect pee? And what's the practical application of this work? Maybe, maybe one day these ideas, these principles could help us design more efficient water ejector systems to our smartphones, our watches, and hearing aids. But I have to be honest, that's not really why I obsess over insect pee for the last four years.

I do this because when I share my work with kids, it ignites their curiosity. When I talk about insect pee, it makes their eyes light up. They'll laugh. They'll run around in their backyards looking at bugs and asking questions. It reminds them and us that we can discover marvelous in the mundane, even in our own backyards. We just have to look closely. Thank you so much.

Additional support from Isabella Aslarona, Daniela Balareso, Valentina Bojanini, Banban Chang, Christopher Faisie Bogan, Cinnamon Horn, Laney Lott, Matthew Polis, and Yadi Vasquez. Learn more at podcasts.ted.com. I am Elise Hu. Thanks for listening.