Tardigrade facts for kids
Quick facts for kids Tardigrada |
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| The tardigrade Hypsibius dujardini | |
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Tardigrada
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Tardigrades, commonly known as 'water bears' or 'moss piglets', are tiny, eight-legged creatures, usually smaller than the tip of a pencil, famous for their incredible ability to survive in extremely harsh conditions that would kill almost any other living thing.
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What do they look like?
Most tardigrades are only about 0.1 to 0.5 millimeters long when they are fully grown. That's smaller than a grain of sand! Some of the biggest ones might reach up to 1.3 millimeters, but you still need a microscope to see them clearly.
They have eight legs, arranged in four pairs. Each leg usually has little claws or sticky pads at the end, which help them move around. Their bodies are covered in a tough outer layer called a cuticle, which they shed and replace as they grow, just like some insects.
Inside their bodies, they have a simple system. They don't have lungs or blood vessels like we do. Instead, they get oxygen and nutrients by absorbing them through their skin. They are made up of only about 1000 cells, which is very few compared to the trillions of cells in a human body!
Where do they live?
Tardigrades are found almost everywhere on Earth. They live in mountains, deep in the ocean, in tropical rainforests, and even in the freezing cold of Antarctica. They are especially common in damp places like mosses and lichens, which are those 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 be carried long distances by wind or on the feet of other animals. This helps them spread to new places. Some types of tardigrades live only in specific areas, like certain mountains or cold seas, while others are found all over the world.
In some places, like on mosses, you can find huge numbers of tardigrades – over 2 million in just one square meter. In soil, there can be as many as 300,000 per square meter.
Discovery
The first time a tardigrade was described was way back in 1773 by a German scientist named Johann August Ephraim Goeze. He thought they looked like tiny bears walking around, so he called them "Kleiner Wasserbär," which means "little water bear" in German.
A few years later, in 1776, an Italian scientist named Lazzaro Spallanzani studied them more and gave them the scientific name "Tardigrada." This name comes from Latin words that mean "slow walkers," which 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. Over the years, many more scientists have studied and classified different types of tardigrades, helping us understand these amazing creatures better. Today, there are about 1,500 known species of tardigrades.
How do they move?
Even though they are called "slow walkers," tardigrades can move around using their eight legs. Their legs work using muscles that pull against each other, similar to how our muscles work. The claws or sticky pads on their legs help them grip onto surfaces as they walk.
What do they eat?
Tardigrades eat by sucking up fluids from other tiny living things or from dead plant and animal material (detritus). They have a pair of sharp little tools called stylets that they use to poke holes in their food, like 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 they 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, while others might be oval or have interesting shapes on their surface.
Some types of tardigrades seem to be all female and 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 that help them survive if things get dry. If they live in water, they might stick their eggs to something or leave them inside their old shed skin. The eggs usually hatch within about two weeks, and 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 conditions that would kill almost any other animal. They aren't really adapted to live in these extreme places all the time, but they can endure them by going into a special state called cryptobiosis.
When their environment dries out, like when the moss they live in dries up, terrestrial and freshwater tardigrades can pull in their legs and curl up into a tiny, dry ball called a "tun." In this tun state, they basically stop all their body processes – they don't need food or water, and their metabolism slows down to almost nothing. They can stay like this for years.
While in the tun state, they become incredibly resistant to extreme temperatures, from super cold (like -272°C, which is almost absolute zero) 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, and even withstand high levels of radiation.
Scientists used to think this survival ability was due to a special sugar, but now they know that tardigrades make unique proteins that 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 even sent tardigrades into outer space. In 2007, dehydrated tardigrades were sent on a space mission and exposed to the vacuum of space and even solar radiation. When they were brought back to Earth and given water, many of them woke up and were fine, and some even laid eggs that hatched. This showed that they could survive the harsh environment of space.
How have they evolved?
Scientists study tardigrade fossils and their genes to 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, with fewer legs.
Scientists think that tardigrades evolved from larger ancestors, possibly similar to ancient worm-like creatures called lobopodians. Over millions of years, they became much smaller and developed their unique body plan and incredible survival abilities.
By studying their genes, scientists are learning more about how their bodies are structured and how they are related to other groups of animals, like insects and spiders.
In popular culture
Because of their amazing toughness and unique appearance, tardigrades have become quite popular. They are often called "charismatic" by scientists 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 and crochet patterns!
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 based on a tardigrade that has special abilities related to space travel, inspired by the real tardigrade's toughness. Musicians have written songs about them, and they've even appeared in movies.
In 2025, a specific species of tardigrade called Milnesium tardigradum was voted the winner of The Guardian newspaper's "Invertebrate of the Year" competition. The article mentioned how this species has survived all five major extinction events in Earth's history, which really highlights their incredible resilience.
Interesting facts about tardigrades
- Approximately 83% of known species live on land, while 17% are aquatic.
- Scientists believe tardigrades diverged from their closest relatives in the Cambrian more than 500 million years ago.
- There are over 1,000 species of tardigrades.
- Tardigrades can survive more than ten years without water.
- They may molt up to 12 times.
- In 2019, tardigrades on a lander that crashed on the moon are believed to have survived and could potentially live there for a few years.
Images for kids
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Tardigrade anatomy
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Shed cuticle of female tardigrade, containing eggs, each 50μm across
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Richtersius coronifer in active and 'tun' states.A↔P = anterior-posterior; mg = midgut; go = gonad;pb = pharyngeal bulb; mo = mouth; st = styletScale bars = 100 μm
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The 2007 FOTON-M3 mission carrying the BIOPAN astrobiology payload (illustrated) exposed tardigrades to vacuum, solar ultraviolet, or both, showing their ability to survive in the space environment.
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Tardigrade body plan compared to arthropods, onychophora, and annelids. Tardigrades have lost the whole middle section of the ecdysozoan body plan, and its Hox genes.
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The 'Ripper' in Star Trek: Discovery is a recognisably tardigrade-like creature enlarged to monstrous size, with extraordinary capabilities said in the TV series to have been acquired by horizontal gene transfer.
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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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The luolishaniids from the Cambrian and Ordovician are possibly the closest fossil relatives of tardigrades. Entothryeos reconstruction shown.
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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 mya)
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Tardigrade sculpture Noah's Ark 3.0 by Arno Coenen, St Eusebius' Church, Arnhem, the Netherlands
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Tardigrade soft toy
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See also
In Spanish: Tardigrada para niños
