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On the surface of the Red Sea, bugs are born, die, and, somewhere in between, make love.
Sea skaters of the genus Halobates are the only insects known to spend their entire lives on the open ocean, skittering like ballerinas on sea foam. But this life is a treacherous one: when they’re not sizzling under ultraviolet radiation or dodging seagull beaks, the ocean’s roiling waves are pulling them under.
These insects need to be well equipped to handle their turbulent environment. Now, a study from scientists at the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia sheds new light on how they manage to stay afloat.
“There’s only one thing in the world like Halobates,” says Lanna Cheng, a marine biologist emeritus at Scripps Institution of Oceanography at the University of California San Diego, and a coauthor of the study. Cheng has studied Halobates for more than 40 years, and is the world’s leading—perhaps only—expert on the little-known oceanic insects. “They live on the open ocean 24/7, under sunlight, with no place to hide.”
Marine skaters are one-third the weight of their freshwater cousins, the spindly, pond-skipping water striders. Both belong to the family Gerridae, of which Halobates is the only marine genus. Though Halobates was first described in 1822, the question of how the genus came to colonize the open sea has remained a mystery, as it seems to have evaded the fossil record.
To find out, the researchers at KAUST first had to keep the enigmatic bugs alive in the lab, which proved to be an unexpected challenge. Gauri Mahadik, the study’s lead author and a former postdoctoral researcher at KAUST, housed the insects in a tank filled with approximately five centimeters of seawater, sargassum seaweed, and some fish food. The skaters took to the tank but not to the food, and soon began eating each other—though it resembled something else. “It looks like they’re having sex, mounted on top of each other,” she says. “But the one underneath is shrinking as its liquids are being sucked out.”
Eventually, Mahadik found that the skaters would eat brine shrimp. But the scientists also quickly learned that once they’d eaten their fill, the insects saw no need to stay in the tank. “You put them in a petri dish, and they could jump a foot,” says Himanshu Mishra, a bioengineer at KAUST and coauthor of the paper.
Once the scientists finally got the skaters to stay put, they managed to identify several evolutionary strategies that help Halobates survive in water that would drown any other insect. For one, they’re incredibly agile; when the researchers showered them with water droplets, they would dodge, jump, and somersault to stay dry.
Mahadik spent countless hours photographing and filming the insects, which highlighted how the skaters survive when they get dunked. By trapping a thin layer of air inside specialized mushroom-shaped hairs, the insects can breathe while entirely submerged. Mahadik also observed the insects grooming themselves, a behavior never before seen in Halobates. By using their forelegs to rub a waxy secretion over their bodies, the insects rid themselves of debris and keep their hairs aligned so they stay as dry as possible.
Mishra thinks the design of these hairs could be used to build more water-repellent objects, such as pipes that carry liquids over long distances. “If you could create microtextures in the pipes so that the liquid is essentially floating on air, there will be less drag,” he says.
David Hu, a fluid dynamicist at the Georgia Institute of Technology who reviewed the paper, says despite new observations and great visuals, it doesn’t definitively answer the question of how Halobates conquered the high seas. “That will take experiments observing Halobates in the open ocean or simulating crashing waves in the lab.”
The researchers have applied for more funding to continue their research, but Mishra says that if the funding doesn’t work out, they’ll find a way to keep studying the charismatic Halobates. “We want to learn their secrets,” he says.