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- 0.5 millimeter
Tiny, but tough
In fact, these invertebrates are so tiny, you need a microscope to be able to see them. But despite being smaller than a poppy seed, tardigrades look pretty fierce when you view them up close: They have claws like bears and daggerlike teeth that tear into and suck the juices out of moss and algae. They’ve even been nicknamed “water bears” for their resemblance to the furry predators.
Tardigrades can be found almost anywhere on Earth, from the top of the Himalaya mountain range to the bottom of the sea, from icy Antarctica to bubbling hot springs. The teeny-tiny creatures can survive extreme temperatures, ranging from minus 328°F up to 304°F. Tardigrades need only a drop of water to thrive.
No water? No problem.
Without access to water, a tardigrade will curl up into a dry ball called a tun. Their body systems slow down so much that they’re almost—but not quite—dead. The tiny animals can survive like this for decades. Scientists call this extreme type of hibernation “cryptobiosis.”
When they’re re-exposed to water, tardigrades can come back to life in just a few hours. Once, when dried moss that had been in a museum for a hundred years was moistened, tardigrades inside the moss came crawling out, totally fine.
Tardigrades spend most of their time snacking on plants and bacteria. They have to be careful, though. Although tardigrades can survive extreme conditions, they still have predators. Nematodes (a kind of worm), amoebas, and sometimes even other tardigrades all prey on tardigrades.
Bears in space
Tardigrades haven’t only survived extreme conditions on Earth. They’re the first animals to survive the vacuum (that means no air), radiation blasts, and freezing temperatures of space.
In 2007, scientists placed the tiny critters into a satellite and shot them into space. There they floated in special containers 167 miles above sea level for 10 days before plummeting back to Earth. Upon inspection, most of the water bears were OK. They had survived radiation blasts 700 times stronger than the sun’s rays on Earth.
Tardigrades are helping scientists rethink what they know about what it takes to survive in extreme conditions—and what humans might need to survive on another planet.
• Tardigrades have been on Earth for about 600 million years, about 400 million years before dinosaurs.
• Tardigrades are sometimes called “moss piglets.”
• Tardigrade eggs take between 40 and 90 days to hatch.