Jumping Droplets Help Cicadas Clean their Wings

Researchers have now found how cicadas keep their wings clean. The study, researchers said, will help design new type of self-cleaning materials.

The cicadas are all set to emerge from their 17-year sleep this spring along the East Coast. Most common species of the insect emerge from the ground on a yearly basis, while some take almost two decades to emerge.

The wings of cicadas have many tiny bumps of varying sizes. When a water droplet lands on the wing, it actually stays on the tip of the bump, on a cushion of air that's tapped underneath.

Researchers found that the cicadas keep their wings clean by a phenomenon where droplets gather dirt from the wings of the insects. Lead author of the study Chuan-Hua Chen, from the Duke's Pratt School of Engineering, called the phenomenon as "jumping droplets".

Researchers used high-speed video imaging to capture these jumping droplets on the wings of the cicadas.

"Most cicadas are unable to clean their own wings because of their short appendages. Furthermore, these insects commonly live in areas where there is little rain over an extended period of time. However, the areas are humid, which provides the tiny dew droplets needed to 'jump clean' their wings," said Gregory Watson of James Cook University.

The ability of currently used materials that repel dirt depends on factors like the angle at which water is falling on it, Chen said. This affects the feasibility of using self-cleaning superhydrophobic surfaces for practical purposes.

"We have found, however, that the self-propelled jumping motion of the dew drops is very effective in dislodging contaminating particles, regardless of the orientation," Chen said in a news release. "These new insights can help guide the development of man-made surfaces that are not dependent on any external forces and are therefore truly self-cleaning."

The study is published in the journal Proceedings of the National Academy of Sciences. The study was supported by the National Science Foundation, the Defense Advanced Research Projects Agency and the North Carolina Space Grant.