Why do cicadas shoot urine in jets instead of simple droplets?
In short: Most small animals and insects excrete waste in droplets to save energy. However, researchers studying cicadas discovered a surprising exception to this rule. By observing these insects in the wild, scientists have uncovered a fluid dynamics phenomenon that challenges everything we thought we knew about how small organisms manage waste.
For years, biologists operated under two main paradigms regarding insect excretion. First, it was assumed that xylem feeders—insects that consume sap—would excrete waste in droplets because it requires less energy. Second, it was believed that small animals were physically limited to droplets because their tiny orifices make it difficult to overcome surface tension and viscous forces to create a high-speed stream.
Saad Bhamla, an assistant professor at Georgia Tech, and his research team set out to study the fluid excretion of the cicada. While the team initially relied on YouTube videos, a field trip to Peru allowed them to witness the process in person. This observation disproved existing theories. Unlike most small insects, cicadas emit jets of urine rather than sprinkling droplets.
The reason for this behavior is rooted in the insect's voracious appetite. Because cicadas consume massive amounts of xylem sap, flicking away individual droplets would be too energy-intensive and would prevent them from extracting enough nutrients. Instead, they use jets to manage the high volume of fluid. While smaller animals struggle with the energy required to force fluid out at high speeds, the larger size of the cicada allows it to utilize gravity and inertial forces to maintain these jets.
This discovery, published in the Proceedings of the National Academy of Sciences, provides a new understanding of fluid dynamics that spans from microscopic fungi to colossal whales. Beyond biology, these findings regarding how fluids are ejected could eventually assist engineers in designing more efficient small nozzles and advanced robotic systems.
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Sources
- Summary by Intellect · source: What Do Insects Do When Nature Calls? | Saad Bhamla | TED
- Also: How do insects pee? A seemingly silly question that led to a physics discovery
- Also: Cicadas' unique urination unlocks new understanding of fluid dynamics
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