Introduction to Tardigrades

Jaime Jiménez was examining moss samples he had collected on a research trip to Chile when he noticed something unusual. Tiny creatures shaped like sausages, with eight stubby legs and a tubular face, were wriggling around under the microscope, looking like animals dreamt up by a children’s book illustrator.

Jiménez, a wildlife ecologist by training and professor at the University of North Texas, had never seen anything like them. Few people even know about these critters, which he learned were tardigrades, a kind of organism found around the globe, often near water.

That chance discovery in 2019 sent Jiménez down a new path of exploration. He has since identified about 80 species of tardigrades in his native Chile, helping to build recognition around these masters of survival that can endure freezing temperatures, radiation and the vacuum of outer space. Their extreme abilities could ultimately inform fields such as medicine, space travel and biodiversity.

What are Tardigrades?

Barely a millimeter long, tardigrades have endured on Earth for more than 550 million years, predating the dinosaurs. Some are aquatic and live in water, while others dwell in mosses and lichens on the ground, Jiménez said: “If you collect plants, you collect them.”

Tardigrades were first discovered in 1773 by a German zoologist and pastor in a pond behind his church. Struck by their pudgy form, he dubbed them “water bears.”

Later that century, an Italian priest and scientist noted the animals’ peculiar, lumbering gait, which would earn them the scientific name Tardigrada, or “slow steppers.”

That scientist also observed how these animals can survive being completely dried out. They do so through a process called cryptobiosis, which entails squeezing out more than 95% of the water in their bodies, retracting their head and legs and curling into a dried-out ball, Jiménez said. They stop using almost any energy while in this state and can survive like this for several decades. With a drop of water, they spring back to life.

Tardigrades’ near invulnerability to radiation could help inspire more effective cancer treatments that avoid harming healthy cells.

Jaime Jimenez

Scientists once thought tardigrades survived extreme dryness by using a sugar to turn their cells into a glass-like state that protects proteins from damage. (For reference, a tardigrade’s body is made up of 1,000 cells, whereas a human body has trillions.)

But a 2017 study revealed a different trick: tardigrades rely on flexible proteins described by researchers as “wiggly spaghetti springs” that constantly shift shape.

That survival skill may have protected tardigrades from Earth’s great mass extinctions. A 2024 study reexamining tardigrade fossils suggests these animals split into their two major groups much earlier than previously thought, likely more than 400 million years ago, when the largest extinction event occurred. The findings hint that water bears adapted to land more than once in their history, and that cryptobiosis may have evolved multiple times.

Teeny but Packing a Scientific Punch

Tardigrades are informing a wide range of scientific fields. One area of research is exploring how to harness the animal’s unique survival techniques.

The same 2017 study that looked at the tardigrades’ flexible proteins suggested these could help stabilize fragile, protein-based medicines that must be kept cold during shipping and storage — a costly task, especially in developing countries. By mimicking the tardigrade’s strategy, medicines could one day be stored and transported at room temperature, making lifesaving treatments far cheaper and more accessible worldwide, NPR reported.

Using these proteins, Jiménez said, could help realize a future envisioned by some scientists, one in which embryos or other organisms are dry-frozen and transported to the moon — or beyond the galaxy — remaining alive for years without the need for nutrients to sustain them.

Those proteins may also hold clues to a biological fountain of youth. A 2024 study found that one type of these proteins slowed metabolism in human cells grown in lab dishes, hinting at a potential way to delay aging.

“Amazingly, when we introduce these proteins into human cells, they gel and slow down metabolism, just like in tardigrades,” said Silvia Sanchez-Martinez, a senior research scientist at the University of Wyoming’s Department of Molecular Biology, who led the study, in a statement last year.

“Just like tardigrades, when you put human cells that have these proteins into biostasis, they become more resistant to stresses, conferring some of the tardigrades’ abilities to the human cells,” she said.

UNT’s Jaime Jiménez collects tardigrade samples from a tree on Navarino Island