Why Fly or Swim When You Can Jump? Ask the Springtail.

8th November, 2022.      //   General Interest  // 

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Springtails are about the size of a pinhead, but they can control their jumps like seasoned acrobats.

Among the wonders of the natural world that few people have ever noticed: a semiaquatic springtail in motion.

There are around 9,000 known species of springtails — small flea-like invertebrates — around the world. Many live in dark, humid habitats, but they can be found on all seven continents; some even migrate over snow. The arthropods rove the earth by flinging their bodies into the air, sometimes rotating 500 times per second, like circus performers shot out of self contained canons. But good luck getting a look at their trapeze show — most springtails are “as small as a grain of sand,” said Víctor Ortega Jiménez, a biomechanics researcher at the University of Maine who has studied the creatures.

Now, a series of slowed down, zoomed-in videos of these high octane jumps, released by Dr. Ortega Jiménez and colleagues in an article published on Monday in the journal Proceedings of the National Academy of Sciences, reveals an element of tiny bodily control that is almost graceful. The visuals aid a detailed explanation of how springtails jump through the air and end up on their feet nearly every time they land.

Dr. Ortega Jiménez said the springtails’ control largely came from their most distinctive and enigmatic feature, the collophore, a tube sticking out of their abdomens. This tube interacts in nuanced ways with the forces around the animals: drag, surface tension, gravity. “They are taking advantage of the water and the air,” Dr. Ortega Jiménez said.Springtails are not insects, although they were classified that way for a long time because of their six legs, segmented bodies and antennae. Because of their mouths, which are retracted inside their heads, they now make up the majority of a different taxonomic class: entognatha.

Taxonomically, springtails are called Collembola, a label given to them by John Lubbock, an English polymath of the 19th and early 20th centuries. The word comes from the Greek words for “glue” and “peg.” Lubbock chose the name from the behavior he observed after he flipped springtails onto their backs and hovered a piece of glass above their stomachs. The animals would reach for the shard with their legs while simultaneously emitting a fluid from the tips of their collophores and pushing it toward the surface. This fluid, Lubbock wrote, “no doubt, gives a better hold.”

Other scientists later disputed this explanation of the collophore’s function. In the 20th century, the most widely accepted functional explanation for the collophore — the only part of the springtail’s body that attracts water — was as a way to suck up nutrients. Other uses were proposed in the 21st century: It could be a self-cleaning tool or a way to direct the springtail’s jump.

Dr. Ortega Jiménez, whose research focuses on how animals move, became interested in springtails when he saw them hopping around near a stream. While it was thought that the animals could only point themselves in a direction and then flip wildly through the air, when the arthropods jumped from the bank into water and back, Dr. Ortega Jiménez noticed that they seemed to land exactly where they had started. Doing so would require some kind of control throughout the entire jump.Heading back to the lab, Dr. Ortega Jiménez started filming springtails in flight, and he designed a small wind tunnel to see how the animals dealt with different aerial conditions. He found that a springtail’s collophore was involved in all parts of the jump.

During the takeoff, when the springtails smacked their tail-like furculae off the water, the collophores picked up a drop of water. As the animals spun around through the air, they curved their bodies into a U shape, which slowed their spinning and eventually allowed them to fly through the air straight, like mini superheroes.

When flipped upside down while in the wind tunnel, springtails with water droplets on their collophores were able to flip themselves around in less than 20 milliseconds, faster than any animal previously recorded. Chests out, the springtails landed, and the watery collophore gave them a more stable base and a sticky adherence to the surface.

“They were skydiving, and they were landing on their feet,” Dr. Ortega Jiménez said.

Using mathematical models, the researchers found that springtails with water droplets on their collophores flopped around much less when they landed than dry springtails; they could end up on their feet in half the time. Saad Bhamla, a biomechanics researcher at the Georgia Institute of Technology who also worked on the research, said that, though there were probably other functions of the collophore, its role in jumping — during takeoff, flight and landing — seemed to be crucial. “That, to me, is the fantastic feature here,” he said.

Dr. Bhamla helped to bring in roboticists, who designed a robot based on the springtail that could right itself in the air and land on its feet 75 percent of the time. This kind of control, he said, has been understudied in robotics, which is often focused on the takeoff. Building a machine that can consistently land on its feet means building a machine that can be ready to jump sooner. “Because if they can control the jump, then they can keep doing it again and again,” Dr. Bhamla said. “And that’s so much more interesting.”

This, Dr. Ortega Jiménez said, could also offer an evolutionary explanation to the springtails’ jumps. While there is much speculation at this point and “the evolution of these jumping animals is a mystery,” a quick recovery from a jump allows the springtails to better escape from predators. “Being ready is essential for survival,” Dr. Ortega Jiménez said.

It surprised the researchers to find so much control in such tiny animals. But dynamics on small scales are often counterintuitive, and even basic features can be easily overlooked. A little bit of water on the abdomen can change everything.

“Design motif-wise, it’s so ridiculously simple,” Dr. Bhamla said. “It’s, like, ‘Why didn’t I think of this?’”

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