Tardigrade. Moss piglet. Waterbear. Whatever you call it, you have to admit that this microscopic creature, known as the “hardiest animal on Earth,” is cute. Weirdly cute. That is, if you can actually see one.
This eight-legged, aquatic animal rarely exceeds one millimeter in length. (That’s about .04 inches, in case you’re metrically challenged.)
Tardigrades were discovered by people in 1773, and in 1776 an Italian biologist dubbed them tardigrada, which means “slow stepper.” Their slow, lumbering gait resembles that of a bear, which explains their more common name.
Scientists have identified more than 1,000 species of tardigrades, which live everywhere on Earth: in salt or freshwater, on moss, in underwater mud — pretty much anywhere they can find water. About 150 marine species have been identified. They feed on fluids from plant and animal cells, as well as on bacteria and even other tardigrades.
Some live in very hot or cold places, such as inside boiling hot springs or under ice. How do they survive harsh conditions — such as insufficient moisture or oxygen, or excessive radiation or pressure or a vacuum state? They curl up into a “tun,” in which metabolic processes slow almost to zero. Also known as cryptobiosis, it resembles death, and a tardigrade can exist like this for decades.
The tun also prevents the formation of big ice crystals, which can damage cells if the temperature drops too far. Tardigrades have been shown to survive freezing to -328 degrees Fahrenheit!
Scientists are so intrigued by this hardy little creature that, in 2007, they put dehydrated waterbears on a rocket to see how they’d do in the vacuum and solar radiation of space. Upon their return 10 days later, 68 percent of the waterbears that had radiation shields survived. Even some of the unshielded ones made it back okay and reproduced successfully.