Saad Bhamla was in his backyard when he noticed something he had never seen before: an insect urinating. Although nearly impossible to see, the insect formed an almost perfectly round droplet on its tail and then launched it away so quickly that it seemed to disappear. The tiny insect relieved itself repeatedly for hours.
It’s generally taken for granted that what goes in must come out, so when it comes to fluid dynamics in animals, the research is largely focused on feeding rather than excretion. But Bhamla, an assistant professor in the School of Chemical and Biomolecular Engineering at the Georgia Institute of Technology, had a hunch that what he saw wasn’t trivial.
“Little is known about the fluid dynamics of excretion, despite its impact on the morphology, energetics, and behavior of animals,” Bhamla said. “We wanted to see if this tiny insect had come up with any clever engineering or physics innovations in order to pee this way.”
Bhamla and Elio Challita, a bioengineering graduate student, investigated how and why glassy-winged sharpshooters – tiny pests notorious for spreading disease in crops – excrete the way they do. By using computational fluid dynamics and biophysical experiments, the researchers studied the fluidic, energetic, and biomechanical principles of excretion, revealing how an insect smaller than the tip of a pinky finger performs a feat of physics and bioengineering – superpropulsion. Their research, published in Nature Communications, is the first observation and explanation of this phenomenon in a biological system.