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After dark, the Watagan Mountains in New South Wales, Australia can appear otherworldly to anyone with a headlamp. But things got stranger than usual in 2015 when John Gould, a behavioral ecologist at the University of Newcastle in Australia, studied sandpaper frogs in ephemeral forest pools for his dissertation.
Dr Gould was crouching on a pool, looking for frogs, when he saw a pea-sized insect he thought had fallen into the water. As he took a closer look, Dr Gould realized he was not looking at an upright insect struggling to escape the water, but an upside down beetle totally in control of its life. and its current situation. He glided under the surface of the water as in a parallel world, Dr Gould kneeling beneath him.
The surface of the pool was immaculate, with no ripple wind in sight, and Dr. Gould pulled out his phone to record the nonchalant crawl from the scavenging beetle’s ceiling. Because the footage was unrelated to his research, Dr Gould stored the video of the beetle in his files and did not return to it for several years as he completed his doctorate. Finally, in June, Dr Gould and Jose Valdez, wildlife ecologists at the German Center for Integrative Biodiversity Research in Leipzig, published the first detailed documentation of this behavior in beetles in the journal Ethology.
Martin Fikáček of National Sun Yat-sen University in Taiwan was not involved in the initial research, but identified the insect as a scavenging beetle, possibly from the Hydrophilidae family.
Although the article represents the first time that the beetle’s upside down underwater exploration has been recorded in the literature, the behavior has already been reported, according to Manu Prakash, a bioengineer at Stanford University who does was not involved in the research. “It’s a beautiful sighting,” wrote Dr Prakash in an email.
The movements of the water collector differ from the traditional way of walking on the water, which is above it. Sea and water surveyors move on the surface of the water with oar-like legs. With the help of surface tension, some geckos can run on water by rippling their bodies and hitting the surface of the water with their paws.
Underwater, some creatures lead an inverted life. Many are snails. In the ocean, the purple snail clings upside down to the ocean surface with a sticky raft of bubbles that keeps its shelled body afloat. The freshwater snail Sorbeoconcha physidae also relies on the mucus, crushing its foot against the surface of the water to move around. “They use a different mechanism because they don’t have legs,” Dr Valdez said of snails.
In freshwater, some insects called rear swimmers swim upside down, rowing their hairy hind legs underwater. The larvae of the Dixidae water fly, also called meniscus midges, use the hairy structures of their abdomen to attach themselves upside down to the surface of the water.
But these scavenging aquatic beetles do not swim like the back swimmer or larvae. They walk, just as you might imagine a species of land beetle walking on earth, or sliding down your ceiling.
The first question: how?
“It’s a bit of a question mark,” admitted Dr Gould, although he and Dr Valdez have some speculations.
One possibility, the researchers said, is that an air bubble clings to the beetle prone, which could provide upward buoyancy keeping the beetle aloft. Although a bubble so close to the surface seems doomed to burst, the beetle’s bubble remained decidedly full, suggesting that the insect is somehow blocking air from escaping, the researchers say. Beetles that can walk (upright) underwater are known to trap air bubbles between their feet.
The second question: why ??
Although the beetle’s feet seemed to prick the water with every step, its inconspicuous stroll produced no ripple. The researchers suggest that this style of locomotion could help the insect avoid being eaten by anything lurking nearby. “Any predator above the surface can look down and see a bubble instead of a tasty treat,” Dr Valdez wrote in an email.
Moving through the drag, buoyancy and viscosity of water generally requires more energy than moving on land. But the beetle appeared to be able to move around quite easily and even appeared to rest upside down, which seems to suggest that this behavior is not energetically demanding, according to the authors.
But the only way to know for sure would be to take the beetle species to a lab for further research.
Today, Dr. Gould is studying another frog on Kooragang Island, not far from the Watagans, which breeds in man-made swamp ponds around the island’s coal harbors. Nature is less pristine there but still conceals small wonders; recently, Dr Gould saw a slug elegantly twirl down to the ground from the top of a fence like an aerial performer, using a strand of its own mucus as a climbing rope.
And what about this particular beetle? Water scavengers have a short lifespan, so this particular beetle is likely gone, its body returned to the Watagan’s petrichorium scented soil. But other beetles remain, alive and dying and walking on any surface that will hold them back.
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