The fascinating physics of insect pee | Saad Bhamla (re-release)

Glass-winged sharpshooters feed on xylem fluid, a liquid made mostly of water and minerals and low in nutrients. Because that food provides little nutrition, they must drink and excrete continually. The insects also spread bacteria that cause deadly plant diseases, including diseases responsible for millions of dollars in damage to California vineyards.

Saad Bhamla describes how sharpshooters eject urine using a spring-and-latch structure he calls a “butt flicker.” It launches droplets at about 40 g of acceleration. The droplets then travel at roughly 150–200% of the flicker’s speed, a result that was faster than the researchers expected.

Bhamla and his student Elio Chilida proposed that surface tension helps explain the added speed by allowing a droplet to store energy before launch. Tests with droplets placed on a speaker and with a model catapult supported the importance of timing in the process. The explanation is therefore tied to the way a droplet’s surface tension and the flicking motion interact, rather than to the flicker alone.

Surface tension also creates a practical obstacle: it makes the urine droplets adhere to the insect’s body. The sharpshooter must flick them away. This means the same property that may help a droplet gain speed also makes releasing it more difficult.

Sharpshooters eject urine as droplets, while cicadas, which also feed on xylem fluid, urinate in jets. Bhamla raises the insects’ small size as a possible reason for the difference but does not elaborate, so the episode leaves that explanation open.

Bhamla says principles from insect droplet ejection could eventually inform more efficient water-ejection systems in smartphones, watches, and hearing aids. The application remains prospective: the episode presents it as a possible use of the research, not as a technology already developed or deployed.