The Surprisingly Powerful Stream of the “Piss Fly”
The insect commonly known as the “piss fly” (Homalodisca vitripennis) – despite the unflattering nickname – isn’t a fly at all, but a leafhopper related to cicadas and aphids.Measuring 1.5 to 2 cm in length, this insect earns its moniker due to an remarkable characteristic: it urinates frequently and in remarkable quantities.
Like all leafhoppers, H. vitripennis primarily feeds on plant sap, specifically from the xylem – the tissue responsible for transporting water and nutrients. Tho, this sap is remarkably dilute, being composed of approximately 95% water but offering limited nutritional value.Consequently, these insects must consume large volumes of sap to obtain sufficient sustenance.
This high-volume fluid intake leads to an equally high-volume output. “Piss flies” can excrete urine up to 300 times their body weight each day, a stark contrast to humans, who eliminate roughly one-fortieth of their body weight in urine daily.
Recently, researchers at the Georgia Institute of Technology, led by biophysicist Saad Bhamla, investigated how these insects manage such a constant and substantial need to urinate. Their investigation, utilizing high-speed video and microscopy, revealed a surprising and previously unknown biological mechanism.
The team discovered that H. vitripennis employs its “anal stylet” – a small organ – in a unique way. The insect folds this organ downwards, allowing a droplet of urine to form. As the droplet grows to an optimal size, the stylus bends further and then rapidly catapults the droplet, achieving an acceleration force exceeding 40 Gs.
This process demonstrates a phenomenon called super-propulsion, a physical principle previously only observed in laboratory settings. Super-propulsion relies on a resonance effect where a deformable object, like a droplet of liquid, can recover energy from the catapulting motion, resulting in a significantly higher ejection speed than a rigid object.
this marks the first documented instance of super-propulsion occurring naturally in a biological organism. Researchers calculated that utilizing this catapulting mechanism requires four to eight times less energy than simply ejecting urine as a jet. This energy efficiency likely explains why evolution favored this unique adaptation.
As co-author Elio Challita notes,”Excretion is often overlooked…but it is an essential biological function.” The study highlights that even seemingly “silly” biological processes can reveal essential and previously unknown principles of physics and evolution, demonstrating the power of observing the natural world.
