Nature’s Chain Mail: Butterfly Wings Have ‘Armor’ To Shield Against Heavy Rain

ITHACA, N.Y. — Butterflies are usually considered among the most delicate of insects, which is why a new study focusing on their wings is so surprising.

Researchers from Cornell University performed an exhaustive investigation on what happens when high-speed raindrops hit various biological surfaces like feathers, plant leaves, and insect wings. Paramount among their conclusions was the revelation that butterflies’ wings, while seemingly super fragile, actually boast an armor of micro-bumps and a nanoscale wax layer that shatter and minimize the damage caused by rain.

Raindrops are nothing more than an annoyance for you or I, but for butterflies a bad storm could spell doom if they can’t find shelter. The tiny armor surrounding a butterfly’s wings gives the insect a certain degree of protection against both physical harm and hypothermia caused by rain.

While these findings are fascinating in their own right, the study’s authors say the principles behind butterfly armor may make a great blueprint for new products in the future. Creating products and goods for humans based on designs or examples seen in nature is nothing new; biomimicry is responsible for numerous innovations.

“This is the first study to understand how high-speed raindrops impact these natural hydrophobic surfaces,” says senior author Sunghwan “Sunny” Jung, an associate professor of biological and environmental engineering, in a statement.

Like A Bowling Ball Falling From The Sky!

Light rain is, obviously, good for plant and insect life, but heavy rain droplets during a storm can fall at a rate of up to 10 meters per second. When rain is coming down that hard, every droplet may as well be a bullet to vulnerable insects and plants.

“Getting hit with raindrops is the most dangerous event for this kind of small animal,” explains Jung.

In fact, Jung says that the relative weight of a raindrop hitting a butterfly is similar to a bowling ball falling out of the sky and hitting a human. Ouch.

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A collection of feathers, leaves, and insects were gathered for this study. All of the samples were then placed on a table, where drops of water fell onto them from a height of roughly two meters. As that was happening, the impacts were recorded and measured using a high-speed camera capable of capturing thousands of frames per second.

‘Micro-bumps’ Secret To Safety For Butterflies

Typically, whenever a drop of water hits a surface it ripples and spreads. The butterfly wing’s nanoscale wax layer, however, repelled falling water droplets. Simultaneously, the microscale bumps poked holes in the raindrop as it made contact with the wing. These two mechanisms combined to greatly reduce the impact and damage inflicted by the simulated rain drops.

“Consider the micro-bumps as needles,” Jung comments.

The micro-bumps also block the rain drops from transferring too much temperature to the wings, which is important because a butterfly’s wings must be at a certain level of warmth to fly.

“If they have a longer time in contact with the cold raindrop, they’re going to lose a lot of heat and they cannot fly very easily,” Jung notes. “By having these two-tiered structures, these organisms can have a super hydrophobic surface.”

The study is published in Proceedings of the National Academy of Sciences.

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