Some sap-sucking insects can “make it rain.” Known as sharpshooters, they fling droplets of pee while feeding on plant juices. Scientists have finally shown how they create these sprays. The insects use tiny structures that catapult these wastes at high accelerations.
Sharpshooters can do serious damage. The pests slurp hundreds of times their body weight daily. In the process, they can move bacteria into plants that cause disease. Take glassy-winged sharpshooters. They have spread beyond their native range in the southeastern United States. In California, for instance, they have sickened vineyards. And they’ve wreaked havoc on the South Pacific island of Tahiti by poisoning spiders that eat sharpshooters.
A tree infested with sharpshooters sprinkles a steady pitter-patter of pee. This can dampen people walking by. “It’s crazy just to look at,” says Saad Bhamla. He is an engineer at Georgia Tech in Atlanta. That rain of pee got Bhamla and his colleagues hooked on studying how the insects release this waste.
The researchers took high-speed video of two sharpshooter species — the glassy-winged and blue-green types. The video showed the insects feeding and then flinging their pee. The videos also revealed that a tiny barb on the insect’s rear end acts like a spring. Once a drop collects on this structure, called a stylus, the “spring” releases. Off flies the drop, as if hurled from a catapult.
Tiny hairs at the end of the stylus increase its flinging power, Bhamla suggests. That’s much like the sling found at the end of certain types of catapults. As a result, the stylus launches pee with up to 20 times the acceleration due to Earth’s gravity. That’s about six times the acceleration that astronauts feel when they launch into space.
It’s not clear why sharpshooters fling their pee. Perhaps the insects do it to avoid attracting predators, Bhamla says.
The scientists reported their findings in a video published online in the American Physical Society’s Gallery of Fluid Motion. It was part of the APS Division of Fluid Dynamics annual meeting held in Atlanta, Ga., November 18 to 20.
acceleration A change in the speed or direction of some object.
catapult A device for throwing or flinging something into the air.
colleague Someone who works with another; a co-worker or team member.
fluid dynamics The study of liquids and gases in motion.
gravity The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.
insect A type of arthropod that as an adult will have six segmented legs and three body parts: a head, thorax and abdomen. There are hundreds of thousands of insects, which include bees, beetles, flies and moths.
online (n.) On the internet. (adj.) A term for what can be found or accessed on the internet.
physical (adj.) A term for things that exist in the real world, as opposed to in memories or the imagination. It can also refer to properties of materials that are due to their size and non-chemical interactions (such as when one block slams with force into another).
predator (adjective: predatory) A creature that preys on other animals for most or all of its food.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
waste Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.
Meeting: E. Challita et al. Insect pee: Ultrafast fluidic ejection from sharpshooters. APS Division of Fluid Dynamics Gallery of Fluid Motion. 71st annual meeting of the APS Division of Fluid Dynamics, Atlanta, Ga., November 18 to 20, 2018.