Iridescent Cicada Wings Cleaned by Jumping Dew Drops (Video)

First Posted: Apr 30, 2013 09:12 AM EDT

A swarm of cicadas are due to emerge all along the East Coast, waking from their 17-year slumber beneath the Earth's surface. Now, researchers are learning a bit more about these insects. They've discovered exactly how cicadas keep their wings fresh and clean after they pop from the ground.

Cicadas are somewhat large insects--about the size of a large cockroach. After first emerging from the ground, the cicada will be in its nymph stage with a dirty brown carapace and no wings. But it won't be long before it breaks free from its shell and emerges with iridescent wings. It's these wings in particular have to be kept clean so that cicadas can fly and participate in the frenzy of feeding and mating that follows.

So how do they do it? Dew drops, in particular, can be beneficial in cleaning cicada wings and other water-repellant surfaces. On these superhydrophobic surfaces (surfaces that are very good at repelling water), the tiny droplets of water actually "jump" by themselves and carry away contaminants. In order to examine this phenomenon, researchers used specially designed high-speed video imaging in order to catch this "jumping" motion on a cicada wing.

After examining the footage, the researchers found that tiny particles such as pollen can be removed from cicada wings through these droplets. Growing dew drops coalesce together, and the merged droplet jumps off of water-repellant surfaces. The jumping motion itself is automatic, powered entirely by the surface energy initially stored in the dew drops.

"The ability of water-repellant surfaces to self-clean has conventionally been attributed to rain droplets picking up dirt particles," said Chuan-Hua Chen, team leader, in a news release. "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."

Yet it turns out cicadas don't need rainfall. Instead, the researchers discovered that the insects bathe in the tiny dew drops that appear in the early morning hours. These drops of water are highly effective at dislodging particles that might foul the insects' wings.

When thousands of cicadas emerge this spring, remember that while they may be loud and while they may be everywhere, at least they'll be clean.

The findings are published in the journal Proceedings of the National Academy of Sciences.

Want to see a video of the water droplets jumping from a cicada's wing? Check it out here.

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