Water-Repellent Sea Skaters Are 100 Times Faster Than Usain Bolt

KAUST; Xavier Pita

Rachael Funnell 19 May 2020, 15:45

A new study published in the journal Scientific Reports is looking to two species of tiny sea skaters, Halobates hayanus and Halobates germanus, to inform improved water-repellent materials. The researchers discovered the key to the insect’s ability to skirt on the ocean surface lies in its waxy coating and tiny hairs.

"Our multidisciplinary study is the first of its kind to investigate two marine skater species, the ocean-dwelling Halobates germanus and a coastal relative, H. hayanus," said Gauri Mahadik, who worked on the King Abdullah University of Science and Technology (KAUST) study, in a statement. "We wanted to understand how these insects had evolved to survive in harsh marine environments where others failed."

Out in the ocean, sea skaters have a lot to contend with, from crashing waves to harsh weather systems, predatory fish, and birds as well as ultraviolet radiation from the sun. In order to survive such a myriad of assaults, these animals have adapted a specialized anatomical makeup to survive life in the ocean. To learn more, the team captured two Halobates species from the Red Sea and coastal mangrove lagoons at KAUST for observations in the lab.

The team used high-resolution imaging equipment, including ultra-fast videography and electron microscopy, to take a closer look at the insect’s body hairs. They found the shapes, lengths, and diameters of the hairs varied across the body. The sea skaters also appeared to secrete a hydrophobic (water-repellant) waxy substance that they used to groom the specialized hair, preventing them from taking on water.

"The tiniest hairs are shaped like golf clubs and are packed tightly to prevent water from entering between them. This hairy layer, if the insect is submerged accidentally, encases it in an air bubble, helping it to breathe and resurface quickly", said co-author Lanna Cheng, from Scripps Institution of Oceanography at the University of California, San Diego, in a statement.

KAUST; Xavier Pita

The researchers found that the insects essentially went one step beyond walking on water and instead were closer to hovering on air. This was revealed when close inspection showed that in their resting state, less than 5 percent of the sea skaters’ total leg surface is in contact with the water. Video footage also showed how raindrops would mostly roll off the insects’ hydrophobic hairs and those that didn’t were flung off as the sea skaters jumped and even performed somersaults to dry off. Move aside, circus fleas.

Their superpowers don’t stop there. When taking off from the water’s surface, Halobates germanus was observed accelerating at around 400 m/s2, more than 100 times the speed of Usain Bolt who clocks around 3 m/s2. In defense of Bolt, this speedy feat is facilitated by the insect’s tiny size but also in the way it uses the water a bit like a trampoline, bouncing off the surface to boost its jump.

The wax that facilitates these oceanic gymnastics is what most excites materials scientists hoping to harness its properties for liquid repellant technologies, though it’s thought the insect's hair structures could also inform material designs to further boost “waterproof” technologies. Mishra reports that his team are now focusing on one of Halobates’ hairs that is mushroom-shaped to innovate greener and cheaper technologies to reduce the drag of objects moving through liquid.

 

 

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