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Not just you in the night: Tiny bugs use superpropulsion to eject huge volumes of pee

This could have practical applications for human technology, say boffins

Scientists have discovered that the tiny insects commonly known as sharpshooters use superpropulsion to ensure they can efficiently eject the huge volumes of urine they produce each day.

Sharpshooters eat plant sap, which is mostly water and light in nutrients. To consume enough to survive, they might need to emit 300 times their body weight in waste water every day.

Researchers led by Saad Bhamla, assistant professor of biophysics at the Georgia Institute of Technology, chose this biological curiosity for more in-depth study and found an intriguing physical phenomenon at its heart.

Superpropulsion occurs when an oscillating surface propels a drop of liquid at a speed higher than that of the oscillating surface by exploiting the resonant frequency of the droplet.

Sharpshooter insects – which might be just a few millimeters in length – form pee droplets through superpropulsion as a strategy to conserve energy. It's more efficient than other mechanisms of waste disposal, such as producing a jet stream – a method employed by other insects including Cicadidae, of which there are more than 3,200 species worldwide.

In a research paper published in Nature Communications, the researchers describe a series of experiments that show sharpshooters temporarily tune the frequency of their "anal stylus" to the frequency of their pee droplets as a single-shot mechanism.

"Our model predicts that for these tiny insects, the superpropulsion of droplets is energetically cheaper than forming jets, enabling them to survive on an extreme energy-constrained xylem-sap diet," the paper reveals.

Any sentient being might think the research grant was justified on the basis of satisfying intellectual curiosity alone – those who do will find their way to the embedded video no doubt. But the scientists at the helm of this project believe there will be practical applications, in terms of designing energy-efficient, self-cleaning structures and soft engines to generate ballistic motions.

As the paper elaborates, "Our work takes these insights from nature and provides a fundamental framework to implement an energy-efficient superpropulsion mechanism for manipulating elastic objects in synthetic systems ranging from pick and place nano and micro-fluidic devices to smart wearable electronics and soft, elastic robotic engines." ®

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