You mainly know cicadas for their sometimes deafening sound in the summer, but did you know that they have another special feature? They pee in a large stream instead of in small droplets as you would expect given their size. Even robots can learn something from their unique way of urinating.
For years, researchers at… Georgia Institute of Technology Learn more about cicada pee. But that is not so easy, because although the animals make a lot of noise, they are difficult to find in the trees in which they are hiding. That’s why it’s quite an event when you see a cicada urinating. Until now, the scientists had only seen this on YouTube.
What a luck
But when they did fieldwork in Peru they were lucky: they saw a large number of cicadas in a tree…peeing. This moment was enough to prove that cicadas urinate differently than other insects. First, cicadas eat xylem sap. This is plant tissue that transports water and minerals. Most insects that eat xylem urinate in droplets because this requires less energy. But cicadas are such voracious eaters that secreting just one drop over and over again would be too taxing and not enough nutrients would be extracted from the sap.
“The assumption is that it takes more energy for an insect to go from peeing droplets to a jet, because it has to accelerate,” says researcher Elio Challita, who is currently at Harvard.
Small opening, small drops
Second, small animals pee in droplets because their opening is too small to secrete anything thicker. But cicadas are relatively large. Their wingspan can be as wide as that of a small hummingbird. This makes it possible for them to urinate in a stream.
“We used to think that it is very difficult for small animals to produce a jet, because it takes them so much energy to release the liquid at a higher speed. This has to do with surface tension and the viscosity of the liquid. A larger animal, on the other hand, can rely on gravity to urinate,” Challita said.
The cicadas are therefore a real eye-opener when it comes to so-called fluid dynamics, or fluid dynamics, which describes the movement of liquids and gases. Cicadas are the smallest animals that can produce jets at high speed. The insects’ strong beam provides insight into how this works, for example, in large mammals.
A framework
The research thus contributes to years of study into the secretion of fluids in all kinds of species, from microscopic fungi to enormous whales. The resulting framework provides insight into various functions, such as the spraying of poison, the spread of spores, the urination of urine and the excretion of fluid by plants. This can be useful for applications in robotics or drug delivery.
The knowledge can, for example, help in developing jets in small robots or automatic sprinklers. And because there are trillions of cicadas, their fluid secretion can have a significant impact on ecosystems, but this is still completely unknown.
Essential processes of life
“Our research has mapped the fluid secretion of all kinds of animals, across eight orders of magnitude, from small cicadas to large elephants,” says the researcher. “We have identified the fundamental constraints and forces that shape these processes. In doing so, we offer a new view on the principles of excretion, a crucial function of all living systems. This work not only deepens our understanding of biological function, but also paves the way for greater knowledge of the underlying principles that govern the essential processes of life,” it sounds poetic.
In other words, the researchers have attempted to paint a comprehensive picture of how fluids leave plants and animals. And that is also useful in technology, such as the aforementioned robotics. “This work shows that even the way organisms dump their waste can provide new insights into fluid dynamics and stimulate innovation in robotics and a variety of other techniques that require handling fluids on a very small scale.”
