Why fly or swim when you can jump? Ask the Springtail.

Why fly or swim when you can jump? Ask the Springtail.

Among the wonders of the natural world few people have ever noticed: a semi-aquatic springtail in motion.

About 9,000 species of springtails – small flea-like invertebrates – are known around the world. Many live in dark, moist habitats, but they can be found on all seven continents; some even migrate over snow. The arthropods roam the earth throwing their bodies in the air, sometimes spinning 500 times per second, like circus performers being shot from self-contained cannons. But good luck watching 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 slow-motion, zoomed-in videos of these high-octane jumps, released by Dr. Ortega Jiménez and colleagues in an article published Monday in the journal Proceedings of the National Academy of Sciences, reveals an element of minor bodily control that is almost graceful. The images help provide a detailed explanation of how springtails leap through the air, landing on their feet almost every time they land.

dr. Ortega Jiménez said the springtails’ control came largely from their most distinctive and enigmatic feature, the collophore, a tube protruding from their abdomens. This tube interacts in a nuanced way with the forces surrounding the animals: resistance, surface tension, gravity. “They take advantage of the water and the air,” said Dr. Ortega Jimenez.

Springtails are not insects, although for a long time they were classified as such because of their six legs, segmented bodies and antennae. Because of their mouths, which have been retracted into their heads, they now make up the majority of another taxonomic class: entognatha.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 “pin”. Lubbock chose the name from the behavior he observed after throwing springtails onto their backs and floating a piece of glass above their bellies. The animals would reach for the shard with their paws while simultaneously expelling a liquid from the tips of their collophores and pushing it to the surface. This liquid, Lubbock wrote“no doubt gives a better grip.”

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 absorb nutrients. Other uses were proposed in the 21st century: it could be a self-cleaning tools or a way to target the jump of the springtail.

dr. Ortega Jiménez, whose research focuses on how animals move, became interested in springtails when he saw them hopping around a stream. While it was thought that the animals could only point themselves in one direction and then spin wildly through the airAs the arthropods jumped from the bank into the water and back, Dr. Ortega Jiménez noted that they seemed to land exactly where they had started. This would require some form of control throughout the jump.

When he returned to the lab, Dr. Ortega Jiménez filming springtails in flight, and he designed a small wind tunnel to see how the animals coped with different air conditions. He found that a springtail’s collophore was involved in all parts of the jump.

During takeoff, as the springtails knocked their tail-like furculas off the water, the collophores absorbed a drop of water. As the animals rotated through the air, they curved their bodies into a U-shape, slowing them down and eventually allowing them to fly straight through the air, like mini-superheroes.

When turned upside down in the wind tunnel, springtails with water droplets on their collophores were able to turn themselves in less than 20 milliseconds, faster than any animal recorded before. Boxes out, the springtails landed, and the watery collophore gave them a more stable base and a sticky bond to the surface.

“They were skydiving and they landed on their feet,” said Dr. Ortega Jimenez.

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

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

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

It surprised the researchers to find so much control in such small animals. But small-scale dynamics are often counterintuitive, and even basic functions can be easily overlooked. A little water on the belly can change everything.

“It’s so ridiculously simple in terms of motive,” said Dr. bhamla. “It’s like, ‘Why didn’t I think of this?'”

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