United States (US) scientists who created the first living robots, known as xenobots found out that they can now reproduce, and in a way not seen in plants and animals, reports CNN.

Formed from the stem cells of the African clawed frog (Xenopus laevis) from which it takes its name, xenobots are less than a millimeter (0.04 inches) wide.

The scientists that developed xenobots have discovered an entirely new form of biological reproduction different from any animal or plant is known to science.

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“I was astounded by it,” said Michael Levin, a professor of biology and director of the Allen Discovery Center at Tufts University who was co-lead author of the new research.

“Frogs have a way of reproducing that they normally use but when you … liberate (the cells) from the rest of the embryo and you give them a chance to figure out how to be in a new environment, not only do they figure out a new way to move, but they also figure out apparently a new way to reproduce.”

Scientist Sam Kriegman said that while people may think of large industrial or metallic figures as robots, the term really refers to any machine that does “physical, useful work” in the world.

“We tried to figure out what useful work they could do, and one of the things that we came up with was to clean up the dish,” Kriegman said.

The researchers placed dye particles and silicone-coated iron beads into the petri dish and observed the movement of the little Xenobots, observing that they were piling up the debris, Kriegman said. He described the Xenobots as bulldozers that move around and push stem cells into piles.

“I said, ‘Oh my God, that’s amazing. What happens when they make the piles. What do the cells become when they’re piles?’ We didn’t know,” Kriegman said. “We found out by letting those piles develop over the course of a few days, and then bringing them into a new dish and seeing if they can move.”

This pointed towards the piles becoming “offspring” of the stem cells, growing their own cilia and operating on their own.

He added: “And it turns out that is possible.”

“Most people think of robots as made of metals and ceramics but it’s not so much what a robot is made from but what it does, which is act on its own on behalf of people,” said Josh Bongard, a computer science professor and robotics expert at the University of Vermont and lead author of the study.

“In that way, it’s a robot but it’s also clearly an organism made from genetically unmodified frog cell,” said Bongard.