Tardigrade facts for kids

Quick facts for kids Tardigrada
The tardigrade Hypsibius dujardini
Conservation status
Least Concern (IUCN 2.3)
Scientific classification
Kingdom:	Animalia
(unranked):	Panarthropoda
(unranked):	Tactopoda
Phylum:	Tardigrada

Tardigrades, often called 'water bears' or 'moss piglets', are tiny, eight-legged creatures. They are usually smaller than the tip of a pencil. They are famous for their amazing ability to survive in very harsh places. These conditions would kill almost any other living thing.

What Do Tardigrades Look Like?

Shed cuticle of female tardigrade, containing eggs

Most tardigrades are only about 0.1 to 0.5 millimeters long when they are fully grown. This is smaller than a grain of sand! Some of the biggest ones might reach up to 1.3 millimeters. You still need a microscope to see them clearly.

They have eight legs, arranged in four pairs. Each leg usually has tiny claws or sticky pads. These help them move around. Their bodies are covered in a tough outer layer called a cuticle. They shed and replace this layer as they grow. This is similar to how some insects grow.

Inside their bodies, they have a simple system. They do not have lungs or blood vessels like humans do. Instead, they get oxygen and nutrients by absorbing them through their skin. They are made up of only about 1,000 cells. This is very few compared to the trillions of cells in a human body!

Where Do Tardigrades Live?

Tardigrades are found almost everywhere on Earth. They live in mountains and deep in the ocean. You can find them in tropical rainforests and even in the freezing cold of Antarctica. They are especially common in damp places. These include mosses and lichens. These are the fuzzy or leafy things you see growing on trees and rocks. You can often find them in soil and leaf litter too.

Because they are so small and tough, their eggs and special survival forms can travel far. Wind or other animals' feet can carry them. This helps them spread to new places. Some types of tardigrades live only in specific areas. Others are found all over the world.

In some places, like on mosses, you can find huge numbers of tardigrades. There can be over 2 million in just one square meter. In soil, there can be as many as 300,000 per square meter.

When Were Tardigrades Discovered?

The first time a tardigrade was described was in 1773. A German scientist named Johann August Ephraim Goeze found them. He thought they looked like tiny bears walking around. So, he called them "Kleiner Wasserbär." This means "little water bear" in German.

A few years later, in 1776, an Italian scientist named Lazzaro Spallanzani studied them more. He gave them the scientific name "Tardigrada." This name comes from Latin words that mean "slow walkers." This describes how they move.

Scientists have been studying them ever since. In 1834, C.A.S. Schulze gave the first detailed scientific description of a specific tardigrade species. Today, there are about 1,500 known species of tardigrades.

How Do Tardigrades Move?

Even though they are called "slow walkers," tardigrades can move around. They use their eight legs. Their legs work using muscles that pull against each other. This is similar to how our muscles work. The claws or sticky pads on their legs help them grip onto surfaces as they walk.

What Do Tardigrades Eat?

Tardigrades eat by sucking up fluids. They get these fluids from other tiny living things. They also eat dead plant and animal material (detritus). They have a pair of sharp little tools called stylets. They use these to poke holes in their food. This can be plant cells or even other small animals like nematodes (tiny worms). Then, they use muscles in their throat to pump the liquid food into their gut.

How Do Tardigrades Reproduce?

Most tardigrades have both male and female individuals. They reproduce by laying eggs. The female lays eggs, and the male fertilizes them. The eggs can look different depending on the species. Some are round and bumpy. Others might be oval or have interesting shapes.

Some types of tardigrades seem to be all female. They can lay eggs that develop without needing a male. This is called parthenogenesis.

Females can lay up to 30 eggs at a time. If they live on land, the eggs have tough shells. These help them survive if things get dry. If they live in water, they might stick their eggs to something. They might also leave them inside their old shed skin. The eggs usually hatch within about two weeks. The baby tardigrades use their stylets to break out of the eggshell.

Incredible Survival Skills

One of the most amazing things about tardigrades is their ability to survive. They can live through conditions that would kill almost any other animal. They are not always adapted to live in these extreme places. But they can endure them by going into a special state. This is called cryptobiosis.

When their environment dries out, like when moss dries up, they can curl up. Terrestrial and freshwater tardigrades pull in their legs. They become a tiny, dry ball called a "tun." In this tun state, they basically stop all their body processes. They do not need food or water. Their metabolism slows down to almost nothing. They can stay like this for years.

While in the tun state, they become incredibly resistant. They can survive extreme temperatures. This includes super cold (like -272°C) to very hot (up to +149°C for short times). They can also survive without air, in a vacuum, under very high or low pressure. They can even withstand high levels of radiation.

Scientists used to think this survival ability was due to a special sugar. Now they know that tardigrades make unique proteins. These proteins help protect their cells and DNA from damage when they dry out. Some of these proteins form a kind of glassy shield inside their cells.

Surviving in Space

Because of their ability to survive extreme conditions, scientists have sent tardigrades into outer space. In 2007, dehydrated tardigrades went on a space mission. They were exposed to the vacuum of space and even solar radiation. When they came back to Earth and were given water, many of them woke up and were fine. Some even laid eggs that hatched. This showed that they could survive the harsh environment of space.

How Have Tardigrades Evolved?

Scientists study tardigrade fossils and their genes. This helps them understand how they fit into the tree of life. Tardigrade fossils are very rare. But the oldest ones found are from about 500 million years ago! These ancient tardigrades looked a bit different from the ones today. They had fewer legs.

Scientists think that tardigrades evolved from larger ancestors. These might have been similar to ancient worm-like creatures called lobopodians. Over millions of years, they became much smaller. They also developed their unique body plan and amazing survival abilities.

By studying their genes, scientists are learning more about how their bodies are structured. They are also learning how they are related to other groups of animals, like insects and spiders.

Tardigrades in Popular Culture

Because of their amazing toughness and unique look, tardigrades have become quite popular. Scientists often call them "charismatic." This is because of their clumsy, cute way of walking and their famous ability to survive almost anything.

Their popularity means you can find them on things like clothing, jewelry, and even as soft toys!

They have also appeared in science fiction stories and shows. For example, in the TV show Star Trek: Discovery, there is a large alien creature. It is based on a tardigrade. It has special abilities related to space travel. This was inspired by the real tardigrade's toughness. Musicians have written songs about them, and they have even appeared in movies.

In 2025, a specific species of tardigrade, Milnesium tardigradum, won a competition. It was voted "Invertebrate of the Year" by The Guardian newspaper. The article mentioned how this species has survived all five major extinction events in Earth's history. This really shows their incredible strength.

Interesting Facts About Tardigrades

• About 83% of known species live on land, while 17% live in water.
• Scientists believe tardigrades split from their closest relatives over 500 million years ago. This was during the Cambrian period.
• There are over 1,000 species of tardigrades.
• Tardigrades can survive more than ten years without water.
• They may molt (shed their skin) up to 12 times.
• In 2019, tardigrades on a lander that crashed on the moon are believed to have survived. They could potentially live there for a few years.

Images for kids

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  Tardigrade anatomy

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  Richtersius coronifer in active and 'tun' states.

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  The 2007 FOTON-M3 mission exposed tardigrades to space.

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  Tardigrade body plan compared to other animals.

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  The 'Ripper' in Star Trek: Discovery is a giant tardigrade-like creature.

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  The first drawing of a tardigrade, by Johann August Ephraim Goeze, 1773.

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  Drawing of Echiniscus testudo on a grain of sand by L.M.F. Doyère, 1840.

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  Drawing of Echiniscus sp. by C.A.S. Schultze, 1861.

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  Drawing of Calohypsibius (Macrobiotus) ornatus var. spinifer by Ferdinand Richters, 1900.

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  Entothryeos reconstruction.

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  Tardigrades may be descended from a lobopodian like Aysheaia.

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  Reconstruction of Paradoryphoribius, from the Miocene (23 to 5.3 million years ago).

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  Tardigrade sculpture Noah's Ark 3.0 by Arno Coenen.

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  Tardigrade soft toy.

See also

In Spanish: Tardigrada para niños