Researchers have found how cicadas keep their wings clean, dew drops. Dew drops “jump” on such surfaces, and carry away contaminants.
The researchers used a high-speed video imaging system to capture the jumping dew drops onto a cicada wing. The team from the universities of Duke and James Cook revealed dew drops are beneficial not only in cleaning cicada wings, but other water-repellent, or superhydrophobic, surfaces as well.
“The ability of water-repellent surfaces to self-clean has conventionally been attributed to rain droplets picking up dirt particles,” Lead author of the study Chuan-Hua Chen, from the Duke’s Pratt School of Engineering said in a statement. “For this conventional wisdom to work, rainfall must be present and the orientation has to be favorable for gravity to effectively remove the rain droplets. These limits severely restrict the practical use of self-cleaning superhydrophobic surfaces.”
“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.
Rows of tiny bumps of various heights and widths characterize cicada wings. On this type of bumpy surface, a water droplet only touches the points of the bumps, creating pockets of air underneath the droplet. As they travel across the surface of the wings, the water droplets seemingly float on the air bubbles, the researchers explained.
“We have found 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.”
Cicadas are flying insects typically a few inches long. The species emerge on a yearly basis, with some U.S. species emerging every 17 years. When they dig out from underground as nymphs they molt, shedding their skin to reveal their wings. They then fly off as full-grown cicadas, spending the next four to six weeks searching for and attracting their mates with the distinctive song. After depositing eggs in the ground, the cicadas die and cycle begins all over.
The results of this analysis were published in a recent issue of Proceedings of the National Academy of Sciences (PNAS). The study was supported by the National Science Foundation, the Defense Advanced Research Projects Agency and the North Carolina Space Grant.
Jumping dew drops clean cicada wings
Researchers at Duke University and James Cook University in Australia have shown that dew drops can be beneficial not only in cleaning cicada wings, but other water-repellant surfaces. On these so-called superhydrophobic surfaces, dew drops “jump” by themselves, carrying away the contaminants.
The video shows droplets of water aggregating around particles, then leaping off the surface of a cidada’s wing.
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