Fun Tardigrade Facts: A Guide to the World’s Toughest Animals

Alison Page

Alison Page


Tardigrade Facts

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If you ever heard of a “water bear” or a “moss piglet,” you might think that’s some kind of fish or even a species of aquatic plant. So, what are tardigrades? Can you keep them as pets? And why do they have the reputation as the toughest animals on the planet?

Read this guide to learn some fascinating facts about the incredible tardigrade. 

What Are Tardigrades?

Tardigrades are sometimes called moss piglets or water bears. They are almost microscopic aquatic creatures with flattened heads and plump, segmented bodies, giving them a pig-like appearance. Water bears have eight legs with four to eight digits or claws.

Despite their cute appearance, water bears are pretty much indestructible and are even able to survive in the vacuum of space!


Moss piglets were first discovered in 1773 by German pastor Johann August Ephraim Goeze, a zoologist. Goeze nicknamed the creatures “little water bears.” A few years later, Lazzaro Spallanzani, an Italian biologist, gave the group of animals the name Tardigrada, which means “slow stepper,” and describes the animal’s strange, toddling gait.

According to the Science Education Resource Center at Carleton College, there are currently around 1,300 species of tardigrades within the classification category of the Tardigrada phylum.

Taking It Slow

Tardigrade means “slow-paced.” The name was initially used to describe tortoises but has been the name of these tiny animals since 1800.


Tardigrades are virtually indestructible and can survive in the most extreme conditions. These remarkable animals can cope with extremely low and high temperatures that would quickly annihilate other organisms. 

Believe it or not, some species of tardigrades can even survive exposure to temperatures of -457.87°F and up to an incredible 302°F, albeit for a very short time!

Why Are Tardigrades So Indestructible?

Moss pigs have a very unusual way of ensuring they survive the harshest conditions and extreme environments.

To do so, the animals enter a state called cryptobiosis. During that death-like state, the animals expel more than 95% of the water content in their bodies, the tardigrade’s legs and head retract, and the animals curl up into a dehydrated “tun.”

There are different forms of cryptobiosis that the water bears use to survive, which are triggered by different environmental conditions, such as:

  • extreme temperatures
  • freezing
  • excess salt
  • desiccation
  • lack of oxygen

During cryptobiosis, the moss pig’s metabolic rate slows down to as little as 0.01% of its usual level. Throughout the animal’s tun state, the cells are protected from damage by a range of water-soluble proteins. Those proteins are known as tardigrade disordered proteins or TDPs and are unique to the water bears.

As the tardigrades expel the water from their bodies, the TDP molecules react to create a tough, glass-like cocoon around each individual cell. That hard shell protects the cellular material from damage, enabling the tardigrade to reanimate from its tun when the environmental conditions are more hospitable.


According to research, tardigrade tuns and even eggs can survive for many decades. In 2016, a group of research scientists successfully revived a tardigrade egg and two tuns that had been in a cryptobiotic state for over 30 years.

It might even be feasible to reanimate tuns that have been dormant for even longer than that. In 1948, an Italian researcher allegedly revived a tardigrade tun from a dehydrated clump of moss that was over 120 years old! However, that report is unsubstantiated, and, as yet, no one else has been able to repeat that feat.

In some species of tardigrades, fluorescence can help protect the creatures against the effects of radiation by transforming potentially damaging ultraviolet radiation into harmless blue light.

Can You Keep Tardigrades As Pets?

Tardigrade Facts

In theory, some species of tardigrades can be kept as pets. You might already have a colony of these critters living unnoticed in your fish tank! However, there are plenty of far more visible species of fish and invertebrates that you could keep. The only way you’ll get to enjoy water bears is through a microscope! 

Tardigrade Anatomy

Tardigrades don’t have any bones. Instead, the creature’s body is supported by a hydrostatic skeleton.

A hydrostatic skeleton is basically a fluid-filled compartment that’s also called a hemolymph. Rather like human blood, the hemolymph contains nutrients that support the tardigrade’s needs.

Although water bears don’t have a spinal cord, they do possess a central nervous system. The signal cord sends signals from the animal’s brain to the body, fulfilling the same function as a vertebrate’s spinal cord.

Lack Of Circulation

The moss pig doesn’t have a respiratory or circulatory system. However, moss pigs do have a complete digestive system. The creatures respire by taking dissolved oxygen from the water through the cuticle wall. The water bear’s body has muscles that contract to assist circulation, transporting the nutrients contained in the animal’s hydrostatic skeleton.

Seeing Clearly

It’s thought that these weird little animals see only in black and white rather than color.

How Big Are Tardigrades?

Moss pigs can range in size from 0.002 to 0.05 inches in length, although they generally don’t grow larger than 0.04 inches long, according to the World Tardigrada Database. These tiny creatures have only around 1,000 cells. In comparison, our human body is made up of trillions and trillions of cells!

Can You See Tardigrades With The Naked Eye?

Although water bears are microscopic animals most commonly viewed through a dissecting microscope of 20- to 30- power magnification, they can be seen with the naked eye.

These tiny creatures are about the same size as a period and are also translucent. However, you can sometimes see one of these amazing little animals with your naked eye if the light is right.

Remember that tardigrades are very slow movers, so you’ll have plenty of time to watch them if you can catch sight of one!

Tardigrade Habitat

As you can guess from their name, water bears live in pretty much any environment where liquid water is present.

You’ll find tardigrades living in freshwater lakes and rivers, ponds, and even on the ocean floor. Moss pigs can also live in the watery film covering terrestrial lichens and mosses, hence the tardigrade’s other common name.

These remarkable creatures can live in a wide range of environments. You’ll find water bears surviving in the Himalayan mountains at altitudes over 19,600 feet and at depths of over 15,000 feet below the water surface in the world’s oceans.

Tardigrades can even survive in the harsh, alien environment of outer space.


So, how do tardigrades survive in such harsh environments? 

Well, not all water bears can live in such extreme conditions. However, those that can live in environments that would kill most other animals do so by morphing into a dehydrated spherical structure called a “tun.”

Research has shown that tuns can tolerate temperatures over 300°F and below an incredible -328°F. These remarkable creatures can also survive immersion in boiling liquids, radiation exposure, and even six times the extreme pressure exerted in the deepest oceans.

That same research study showed that some kinds of dehydrated tardigrades in tun form could survive a ten-day trip into low-Earth orbit and revert to their usual form afterward!

You’re Fired!

Remarkably, the indestructible tardigrade has been recorded traveling at almost 3,000 feet per second before withstanding a massive impact of around 1.14 gigapascals of pressure when fired from a high-speed firearm!

That fact raises the tantalizing possibility that several thousand tuns taken on the Israeli lunar mission could even have survived space travel following the lander Beresheet’s crash on the moon’s surface! 

What Do Tardigrades Feed On?

Most tardigrade species feed on the fluids in plant cells, fungus, and algae. The moss pigs use needle-like stylets in their mouthparts to pierce the plant cell walls before sucking up the liquid inside. 

Some tardigrade species eat other living animals, including nematodes, rotifers, and other tardigrades!

Water Bear Reproduction

Adult tardigrades are asexual or sexual, depending on their species.

For the varieties that lay eggs, female tardigrades can produce around 30 eggs each time. Sometimes, the eggs are fertilized inside the female water bear’s body, inside her shed cuticle after the male has deposited his sperm. However, the eggs can sometimes be fertilized while attached to the substrate or sand. 

Other species of tardigrades are self-fertilizing hermaphrodites that can reproduce via parthenogenesis. Parthenogenesis is a process whereby a tardigrade embryo develops without external fertilization.

Tardigrade Gestation Period

Tardigrade embryos are generally completely developed within two weeks of fertilization. However, the embryo’s development can take up to 90 days, depending on the temperature and humidity of the surrounding environment.

Juvenile moss pigs don’t have a larval stage. Instead, the young tardigrades look like miniature adults as soon as they hatch. The only real visible difference is that the juveniles have fewer spines and claws than fully-grown tardigrades.

Juvenile tardigrades go through several growth stages by molting their external skin or cuticle. Each shedding can take from five to ten days to complete.

Are Water Bears An Endangered Species?

Water Bears have yet to be evaluated by the International Union for Conservation of Nature (IUCN).

The IUCN monitors the conservation status of natural habitats and the animals that live there. Animals that are endangered appear on the IUCN Red List, and tardigrades don’t appear on that list at the time of writing.

That’s not surprising when you consider that the humble tardigrade has survived all of the five mass extinctions on Earth since water bears first appeared around half a billion years ago.

Despite their unassuming nature and lack of visibility, it looks highly likely that moss pigs will be thriving on our planet long after the human race has gone extinct.

Final Thoughts

Tardigrades are also known as moss pigs and water bears. These creatures can be found wherever there’s a drop of water and can survive in the harshest environmental conditions, including extreme temperatures, radioactive environments, excessive pressure, and dehydration.

Water bears have been around for millions of years and, according to scientists, are highly likely to be here on Earth long after the human race has gone.

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