The investigator Saad Bhamla He was in the patio of his house when he saw something unusual: a bug peeing. It was about one sharpshooter o leafhopper (Cicadellidae) that formed a tiny and almost perfect round blob on its tail and then released it, almost making it disappear. And it was not the only ‘shot’: she was doing it for hours. This vision intrigued Bhamla, a professor in the Georgia Institute of Technology’s School of Chemical and Biomolecular Engineering, who had a hunch that what he saw was not trivial.
That is why Bhamla, along with Elio Challitaa bioengineering student at the same center, investigated this unknown practice, discovering that they expel their urine through superdrive, a technique that enables them to eliminate amounts of liquid up to 300 times their own body weight per day. The conclusions have just been published in an article in the journal ‘Nature Communications’.
“Little is known about the fluid dynamics of excretion, despite its impact on animal morphology, energy, and behavior,” explains Bhamla himself. “We wanted to see if this tiny insect had developed some kind of purposeful mechanism to urinate in this way.”
small but mighty
The researchers used high-speed video and microscopy to see precisely what was happening in the insect’s tail. They first identified the role played by a very important biophysical tool called ‘anal stiletto‘, which throws the drop in a movement similar to that made by the hand of a basketball player when shooting for a basket.
Challita and Bhamla observed that when the ‘sniper’ is ready to urinate, the anal needle rotates from a neutral position backwards to allow space while the insect squeezes out the fluid. The drop forms and gradually grows larger as the stylet remains at the same angle. As the blob approaches its optimum diameter, this appendage pulls back about 15 degrees and then, like the flippers on a pinball machine, launches the blob at incredible speed, more than the acceleration of a cheetah or athlete Usain Bolt. Furthermore, the authors calculated that it expels gout ten times faster than the fastest sports cars.
“We realized that this insect had evolved a spring and lever like a catapult and that it could use those tools to repeatedly launch drops of urine at high accelerations,” Challita says.
Superdrive: Like a springboard
The researchers then compared the speed of the ‘anal stylet’ with that of the droplet, and found a surprise: Although they assumed the speed would be the same, the data revealed that the droplets were going 1.4 times faster than the movement of this. appendix. Then, the authors realized that this phenomenon corresponded to the presence of superdrive, a phenomenon that had been seen in artificial devices (specifically in the behavior of drops of water that were detached from a larger mass by the action of a plastic ‘tongue’), and which is similar to the extra impulse received by a person who He jumps from a springboard whenever he does it at the right time. In this case, they found that this appendage compresses the droplets, accumulating energy from surface tension, just before launch.
However, there was still an important question in the air: why expel drops and not a continuous stream, like other animals -including other insects-? The answer seems to be found in the diet. Leafhoppers feed only on xylem sage, a nutrient-deficient liquid containing only water and a small amount of minerals. They drink up to 300 times their body weight a day from this liquid, so they are constantly drinking and must also constantly excrete excess water (which corresponds to 99% of the composition of the sap).
Other insects also feed on this sap; however, they excrete powerful spurts. That is why they analyzed samples of the leafhoppers to see what was happening inside them thanks to computerized microtomography. With that information, they calculated the pressure required by the insect to push the fluid through its anal canal and how much energy it needed to do so. The data reveals that the ejection of droplets serves as a strategy to conserve energy in their feeding-excretion cycle. That is to say, due to their small size, urinating the drops costs them less work than urinating a stream.
Leafhopper urination applications
By combining biology, physics and engineering, the research has implications for several fields. Understanding the role of excretion in animal behavior, size, and evolution may have applications to ecology and population dynamics. For example, leafhoppers are a major agricultural pest in California and Florida, spreading diseases in vineyards and citrus groves, causing millions of dollars worth of damage. Their excretions could potentially serve as a vector surveillance tool, as the problem is likely to worsen with climate change. The team’s analysis also highlights the importance of studying excrement processes, as they can reveal a multifaceted perspective on an organism’s behavior.
On the other hand, studying how they use superdrive can also provide insights into how to design systems to repel water, such as smartwatches that repel moisture using speaker vibrations.
“This work reinforces the idea that curiosity-driven science is valuable,” says Challita. “And the fact that we discovered something as interesting as droplet superpropulsion in a biological system, which also has applications in different fields, makes it even more fascinating.”