An eight-legged animal smaller than a grain of sand that can dry out completely, wait for years, and come back to life when water returns. Dried, it shrugs off radiation, crushing pressure and the vacuum of space. Awake, it is surprisingly fragile.

How it survivesReal limits vs myths
PhylumTardigrada
Lives inMoss, soil, sea
IUCN statusNot assessed
DietPlant cells, tiny animals
TARDIGRADES AT A GLANCE

Tardigrades are a phylum of microscopic animals, most under 0.5 mm long, with over 1,400 described species. They live in films of water on moss and lichen, in soil, fresh water and the sea, from the deep ocean to the Himalayas. Many can survive drying out by entering a "tun" state, in which metabolism nearly stops. Tuns tolerate extremes that would kill almost any other animal; active tardigrades do not.

Tardigrades are not insects. This profile sits in our Insects section alongside other small invertebrates. Figures graded and sourced below.
KEY DISCOVERIES
1773First seenJohann Goeze describes a "little water bear" under his microscope.
1776NamedLazzaro Spallanzani calls them Tardigrada, "slow steppers", and revives dried ones with water.
1998Crushing pressureDried tardigrades survive 600 MPa, about six times the deepest ocean (Seki & Toyoshima).
2007Open spaceThe TARDIS experiment exposes tuns to space on a satellite; some survive (Jönsson et al.).
201630 years frozenAnimals from Antarctic moss frozen in 1983 revive and reproduce (Tsujimoto et al.).
2016Dsup foundA tardigrade protein cuts X-ray damage in human cells by about 40% (Hashimoto et al.).
ONLY IN TARDIGRADES

What makes a tardigrade unlike any other animal?

Short answer: Not one trick but a set no other animal combines: its own protective proteins, a glowing sunscreen in some species, regrowable teeth and an unusually trimmed genome.

01A DNA shield found nowhere elseDsup, a protein known only from tardigrades, wraps DNA like a cloud and blocks damage from radicals. Added to human cells in a dish, it cut X-ray damage by about 40%.Hashimoto et al. 2016
02Protein glass instead of sugarMost animals that survive drying rely on the sugar trehalose. Tardigrades use their own protein families, which set into a glass-like solid that holds cells together.Boothby et al. 2017
03A sunscreen that glowsA Paramacrobiotus species from India glows blue under UV light. Its fluorescent pigment absorbs the harmful rays; the pigment even protected nematodes coated in it.Suma et al. 2020
04Teeth that are replaced each moultIts piercing stylets are shed with the cuticle every moult. For a short time the animal cannot eat until a new pair is built.Nelson et al. 2015
05Legs with no jointsIts eight stumpy legs are soft, unjointed lobes, closer to a velvet worm’s than an insect’s. The back pair points backwards to grip moss.Nielsen 2012
06Genes for damage, deletedThe genome of Ramazzottius varieornatus has lost several genes that, in other animals, speed up stress damage. Losing them may be part of the toughness.Hashimoto et al. 2016
FACT SHEET

How small and how tough is a tardigrade?

Short answer: Most are under half a millimetre. In the dried tun state they survive nearly 1,000 times the radiation that kills a person.

MeasuredEstimatedQuoted, unverified
Body lengthMeasured0.05 to 1.2 mm00.51.01.5 mmMost species are 0.3 to 0.5 mm, about the width of a pencil line.Adult size range across the phylum
Described speciesMeasured1,400+One square per 50 species. New ones are described every year.Degma, Bertolani & Guidetti, Actual checklist of Tardigrada
Longest frozen, then revivedMeasured30.5 yearsFrozen moss30.5 yrsTypical active lifemonthsAntarctic moss stored at −20 °C. Tsujimoto et al. 2016
Radiation, tun stateMeasured~4,400 GyTardigrade~4,400 GyHuman, lethal~5 GyGamma rays; dose survived by at least half. Horikawa et al. 2006
Pressure, tun stateMeasured600 MPaTardigrade600 MPaDeepest ocean~110 MPaSeki & Toyoshima, Nature 1998
Heat, tun stateMeasured~83 °C for 1 hTun (50% die)82.7 °CActive (50% die)37.1 °C, 24 hRamazzottius varieornatus. Neves et al. 2020
Impact speed survivedMeasured~900 m/sSurvived0.9 km/sKilledabove ~1 km/sFired from a gas gun into sand. Traspas & Burchell 2021
Survives 151 °CQuoted, unverifiedn/aAn old figure from 1920s experiments, repeated online without the details. Modern tests put the limit far lower.Popular claim
Revived after 120 yearsQuoted, unverifiedn/aFrom a 1948 report of a leg twitch in old museum moss. The animal never recovered; it has not been repeated.Popular claim
THE TUN

How does a tardigrade survive drying out?

Short answer: It enters cryptobiosis: it loses almost all its water, curls into a "tun" and almost stops its metabolism, then restarts when water returns.

01ActiveSwims and crawls in a film of water on moss. Body is mostly water.
02Drying startsSenses water loss. Must dry slowly; sudden drying kills it.
03Curls upPulls in head and legs, shrinks into a barrel-shaped tun.
04TunWater falls to a few percent. Metabolism is barely measurable.
05RehydratesWater returns. It uncurls and walks again within minutes to hours.
AnhydrobiosisDryingThe best known. Triggered by loss of water.
CryobiosisFreezingSurvives ice forming inside or around the body.
OsmobiosisSaltCopes with water that suddenly turns very salty.
AnoxybiosisNo oxygenSwells up rigid and waits, but only for days.
ChemobiosisToxinsProposed for poisons in the water; least studied.
REAL LIMITS

Is the tardigrade indestructible?

Short answer: No. Its records are set in the dried tun state, often by only some individuals. Awake, a tardigrade dies at temperatures a person would barely notice.

HeatActive: 50% die at 37.1 °C over 24 hTun: 50% die at 82.7 °C after 1 hNeves et al. 2020
RadiationActive: ~5,000 Gy gamma, slightly more than tunsTun: ~4,400 Gy gamma; humans die at ~5 GyHorikawa et al. 2006
PressureActive: not tested at these levelsTun: 600 MPa, about six times the Mariana TrenchSeki & Toyoshima 1998
SpaceActive: not testedTun: 10 days in orbit; vacuum alone was survivable, full solar UV killed mostJönsson et al. 2008
Drying speedMust dry over hoursFast drying kills it before the tun formsWright 2001; Boothby et al. 2017
Active animalDried tunResults vary widely between species.
THE MOLECULAR TOOLKIT

What molecules protect a tardigrade?

Short answer: Several families of tardigrade-only proteins. Some turn into a glass-like gel as the animal dries; one shields DNA from radiation.

DsupDamage suppressor. Binds DNA and protects it from radicals. In human cells it cut X-ray damage by about 40%.
CAHS proteinsCytoplasmic proteins that form a gel, then glass, locking cell contents in place as water leaves.
SAHS and MAHSRelated families found outside cells and in mitochondria, thought to protect membranes.
Little trehaloseMany drought-surviving animals use the sugar trehalose. Most tardigrades make little or none of it.
Why researchers care1Vaccines without fridgesCAHS-style proteins kept enzymes working after drying, hinting at storage without cold chains.2Protecting cellsDsup is being tested as a way to shield cells from radiation damage.3Crops and droughtMoving tolerance genes into plants is an early-stage idea, not a result.Hashimoto et al. 2016; Boothby et al. 2017.
SPACE AND IMPACTS

Can tardigrades survive in space?

Short answer: Partly. Dried tardigrades survived 10 days in open space, but most died once full solar UV was added. In 2019, tuns crash-landed on the Moon.

2007TARDIS, low Earth orbitTwo species rode outside the FOTON-M3 capsule for 10 days. Vacuum and cosmic rays alone were survivable; with UV, a few Milnesium tardigradum survived.Jönsson et al. 2008
2019Beresheet, the MoonAn Israeli lander carrying dried tardigrades crashed. Whether any survived is unknown, and they could not revive without water.Oberhaus, Wired 2019
2021The gas-gun testTuns fired into sand survived up to about 900 m/s, but not 1,000 m/s. That speed equals a shock pressure of 1.14 GPa.Traspas & Burchell 2021
BODY PLAN

What does a tardigrade’s body look like inside?

Short answer: Eight stubby legs with claws, a mouth with needle-like stylets, a moulting cuticle and no lungs, heart or blood vessels.

1234Head →
1Stylets and pharynxTwo hard stylets pierce plant cells or prey; a muscular pharynx sucks out the contents.
2Eight legs, four pairsThe back pair points backwards, for gripping. Each ends in claws or sticky discs.
3ClawsShape and number of claws are key to telling species apart.
4Open body cavityFluid in the body cavity carries oxygen and nutrients; there is no heart. Gas passes through the skin.
Like insects, tardigrades moult their cuticle to grow. The cuticle holds chitin and hardened proteins, and new stylets form at each moult.
EVOLUTION

What are tardigrades related to?

Short answer: They belong with the moulting animals. Their closest relatives are arthropods and velvet worms; exactly which is closer is still debated.

Where tardigrades sitRelationships only, not to time scale
RotifersSpiralia; also survive dryingRoundwormsNematodaTardigradesTardigradaVelvet wormsOnychophoraArthropodsInsects, spiders, crustaceansEcdysozoa (moulting animals)Panarthropoda
Rotifers are shown because they share moss and also survive drying, but they are only distantly related. Fossils: tardigrades in Cretaceous amber about 90 million years old, and in Dominican amber (Mapalo et al. 2021).
WHERE THEY LIVE

Where can you find tardigrades?

Short answer: Almost everywhere there is a film of water: moss on a wall, lichen, leaf litter, soil, ponds and ocean sediments, from the deep sea to high mountains and Antarctica.

Moss and lichenThe classic home; dries and wets daily.
Leaf litter and soilAmong grains, alongside nematodes.
Fresh waterPond and lake bottoms.
SeaBetween sand grains, to the deep sea.
PolarAntarctic moss and lake mats.
High mountainsRecorded high in the Himalayas.
Find one yourselfSoak a pinch of dry moss in rainwater overnight, squeeze it into a dish and scan with a simple microscope at 20 to 40× magnification. Look for slow, lumbering movement.
LIFE CYCLE

How do tardigrades reproduce?

Short answer: By eggs. Many species have males and females, but many others are all female and reproduce without mating.

1EggsLaid freely or inside the shed cuticle during a moult.
2HatchIn days to weeks; young look like small adults.
3MoultShed the cuticle, including stylets, to grow.
4AdultMost species live months to two years while active.
5PauseTime spent in a tun does not count, so total age can be far longer.
MYTH OR FACT

Six tardigrade claims, checked

Short answer: The real science is remarkable enough. Most of the exaggeration comes from leaving out the word "dried".

4Myths1Half true1Fact
01MYTH“Tardigrades are indestructible.”WHERE IT CAME FROMHeadlines calling them the toughest animal on Earth.
WHAT THE EVIDENCE SAYSThe records are for dried tuns, often only some survive, and limits vary by species. Active animals die at 37 °C within a day.
WHAT IS TRUE INSTEADExtraordinary at waiting out extremes, not at living through them.Sources: 08, 13
02HALF TRUE“Tardigrades can survive in space.”WHERE IT CAME FROMThe 2007 TARDIS experiment.
WHAT THE EVIDENCE SAYSTuns survived 10 days of vacuum and cosmic rays in orbit. With full solar UV added, most died; a few of one species survived.
WHAT IS TRUE INSTEADThey can survive space for a short time, dried and shielded from UV.Sources: 07
03MYTH“Tardigrades have alien or "stolen" DNA.”WHERE IT CAME FROMA 2015 study claimed 17.5% of their genes came from bacteria.
WHAT THE EVIDENCE SAYSIndependent teams showed most of those genes were contamination from bacteria in the samples. The real figure is small, like other animals.
WHAT IS TRUE INSTEADTheir genome is ordinary animal DNA with some unusual protective genes.Sources: 09, 10
04MYTH“Tardigrades are insects.”WHERE IT CAME FROMThey are often filed with bugs, including on this site.
WHAT THE EVIDENCE SAYSThey have eight legs and belong to their own phylum, Tardigrada, alongside arthropods but not inside them.
WHAT IS TRUE INSTEADMicroscopic animals related to arthropods and velvet worms.Sources: 11
05MYTH“They survive boiling at 151 °C.”WHERE IT CAME FROM1920s experiments, retold without detail.
WHAT THE EVIDENCE SAYSModern tests found half of dried tuns of one species died after an hour at 82.7 °C. Brief exposures to higher heat are survivable, but not boiling for long.
WHAT IS TRUE INSTEADHeat-tolerant when dried, for short periods.Sources: 13
06FACT“Tardigrades revived after 30 years frozen.”WHERE IT CAME FROMA 2016 Japanese study of Antarctic moss.
WHAT THE EVIDENCE SAYSTwo animals and an egg from moss stored at −20 °C since 1983 revived; one animal reproduced.
WHAT IS TRUE INSTEADThe best-documented long-term survival record.Sources: 04
OPEN QUESTIONS

What science still doesn’t know

Short answer: Plenty. Most toughness studies use just a few lab species, so what is true of one tardigrade may not be true of another.

?How do they restart?Nobody knows exactly how metabolism switches back on after years in a tun.
?How many species exist?Over 1,400 are described, but most habitats are barely sampled. The true number could be several times higher.
?Arthropods or velvet worms?Which group is the tardigrade’s closest relative is still unresolved.
?How old is the oldest?The longest verified pause is 30 years. Upper limits are untested.
?Why the variation?Some species tolerate far more than others, even in the same moss. The reasons are only partly known.
?Could they live on Mars?No. They survive some space conditions dried, but need liquid water and food to be active.
FAQ

Frequently asked questions

Are tardigrades really immortal?+

No. Active tardigrades live from a few months to about two years. Time spent dried in a tun pauses that clock.

Can you see a tardigrade without a microscope?+

Only just. The largest are about 1 mm and look like a moving speck. A cheap microscope at 20 to 40× shows them clearly.

Are tardigrades dangerous to humans?+

No. They are harmless and live on moss, lichen, algae and tiny animals.

What do tardigrades eat?+

Most pierce plant, algae or fungal cells with stylets and suck out the contents. Some, like Milnesium, eat rotifers, nematodes and other tardigrades.

Why are they called water bears?+

Goeze named them "little water bears" in 1773 for their lumbering, bear-like walk.

Do tardigrades live in my garden?+

Almost certainly. Moss on walls, roofs and trees is one of the best places to find them.

COMPARE AND EXPLORE

Other animals that cheat death

Short answer: Survival through pausing is rare. Most "immortal" animals regrow or renew instead.

ARTICLEImmortal jellyfishOpen →ARTICLEAxolotl regenerationOpen →TOOLWorld RecordsOpen →TOOLSize ComparisonOpen →
HOW WE KNOW

Sources and how we check

This page is written by Strange Animals and checked against primary research. Every figure carries a grade and a numbered source.

Cite this pageStrange Animals. (2026, November 13). Tardigrade (Tardigrada): cryptobiosis, real limits, space and myths. https://strangeanimals.info/insects/tardigrades/tardigrade
  1. 01Goeze, J. A. E. First description of the "kleiner Wasserbär". Bonnets Abhandlungen aus der Insektologie1773
  2. 02Seki, K. and Toyoshima, M. Preserving tardigrades under pressure. Nature 395: 853-8541998
  3. 03Horikawa, D. D. et al. Radiation tolerance in the tardigrade Milnesium tardigradum. International Journal of Radiation Biology 822006
  4. 04Tsujimoto, M., Imura, S. and Kanda, H. Recovery and reproduction of an Antarctic tardigrade retrieved from a moss sample frozen for over 30 years. Cryobiology 72: 78-812016
  5. 05Hashimoto, T. et al. Extremotolerant tardigrade genome and improved radiotolerance of human cultured cells by tardigrade-unique protein. Nature Communications 7: 128082016
  6. 06Boothby, T. C. et al. Tardigrades use intrinsically disordered proteins to survive desiccation. Molecular Cell 65: 975-9842017
  7. 07Jönsson, K. I. et al. Tardigrades survive exposure to space in low Earth orbit. Current Biology 18: R729-R7312008
  8. 08Traspas, A. and Burchell, M. J. Tardigrade survival limits in high-speed impacts. Astrobiology 21: 845-8522021
  9. 09Boothby, T. C. et al. Evidence for extensive horizontal gene transfer from the draft genome of a tardigrade. PNAS 112: 15976-159812015
  10. 10Koutsovoulos, G. et al. No evidence for extensive horizontal gene transfer in the genome of the tardigrade Hypsibius dujardini. PNAS 113: 5053-50582016
  11. 11Degma, P., Bertolani, R. and Guidetti, R. Actual checklist of Tardigrada species. Università di Modena e Reggio Emiliaongoing
  12. 12Mapalo, M. A. et al. A tardigrade in Dominican amber. Proceedings of the Royal Society B 2882021
  13. 13Neves, R. C. et al. Thermotolerance experiments on active and desiccated states of Ramazzottius varieornatus. Scientific Reports 10: 942020
  14. 14Wright, J. C. Cryptobiosis 300 years on from van Leeuwenhoek: what have we learned about tardigrades?. Zoologischer Anzeiger 2402001
  15. 15Suma, H. R. et al. Naturally occurring fluorescence protects the eutardigrade Paramacrobiotus sp. from ultraviolet radiation. Biology Letters 16: 202003912020
  16. 16Nelson, D. R., Guidetti, R. and Rebecchi, L. Phylum Tardigrada. Thorp and Covich’s Freshwater Invertebrates2015
  17. 17Nielsen, C. Animal Evolution: Interrelationships of the Living Phyla. Oxford University Press, 3rd ed.2012
WATCH

Three films worth your time

ExplainerTED-Ed · Thomas BoothbyMeet the tardigrade, the toughest animal on EarthAn animated lesson on the tun state, by a researcher who studies it.Pairs with: The tun →
ScienceWIREDTardigrade proteins and drying outHow tardigrade proteins may help preserve vaccines and blood without refrigeration.Pairs with: Molecules →
Deep diveReal ScienceThe Insane Biology of: The TardigradeAnatomy, cryptobiosis and the space experiments in one longer film.Pairs with: Space →
SPECIES PROFILES

More species profiles

All profiles →
BIRDS · HUMMINGBIRDSHummingbirdHovering, torpor, 366 speciesMAMMALS · MARSUPIALSKangarooHopping, pouch, mobsMAMMALS · SLOTHSSlothSlowness, fur, seven speciesMARINE LIFE · SEA TURTLESGreen sea turtleNavigation, grazing, recoveryMAMMALS · UNGULATESGiraffeNeck, blood pressure, speciesBIRDS · RAPTORSBald eagleNests, piracy, recoveryPETS · DOGSDomestic dogOrigins, nose, mind, breedsREPTILES · CROCODILIANSSaltwater crocodileBite, sea travel, recoveryPETS · CATSDomestic catDomestication, senses, purringEXTINCT · DINOSAURSTyrannosaurus rexBite, growth, extinctionREPTILES · MONITORSKomodo dragonVenom, iron teeth, islandsMARINE LIFE · WHALESBlue whaleSize, krill, song

All tardigrade articles

1 articles
TardigradesProfile · Jan 28, 2026Tardigrades: Paused at 1 Percent Water