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Claim check

Are tardigrades immortal, and can they survive dried out for a century?

Not supported

No good evidence supports this, or the evidence points the other way.

The century figure traces to one report of a leg moving in a museum specimen, which was not revival. Tested against moss of documented age, survival runs to years and declines steeply.

The claim as it circulates

“Tardigrades can survive without water for over 100 years and are effectively immortal.”

Where you may have met it: Trivia and "immortal animals" listicles, usually alongside the immortal jellyfish; Older popular-science writing, which repeated the figure uncritically for decades; Google autocomplete around tardigrade lifespan

Taking it apart

What was claimed
That tardigrades survive desiccation for over a century, and that this amounts to a form of immortality.
What was actually observed
A critical review traced the century figure to a single unreliable observation of movement in a museum specimen, which was not a demonstration of revival and was not presented as one. Controlled rehydration of dated herbarium moss yielded revival from material up to around nine years old, with survival declining steeply as storage time increased and none from substantially older material. Rotifers and nematodes in the same samples showed the same pattern.
What the evidence supports
Anhydrobiotic survival measured in years, with a small number of credible reports approaching a decade — extraordinary for a millimetre-long animal spending it as dust — and a survival probability that falls progressively with time.
What it does not support
Survival for a century. Nor immortality in any sense: active tardigrades live months to a couple of years, age, and die. Time in the tun does not count against the lifespan, which is the only sense in which anything is paused.

Herbarium collections are the right way to test this and the reason is bookkeeping rather than biology. A sample whose age is remembered can support any number; a dried moss specimen carries a collection date written at the time by somebody with no interest in tardigrades. Rehydrating dated material gives an answer that cannot be talked up.

The decline is the finding worth carrying, and it is more interesting than the headline. If the tun were true suspension, survival would be indefinite. It is not: something accumulates or degrades, slowly, and the chance of coming back falls every year. A very slow leak rather than a pause button — and what exactly is leaking is unresolved.

The claims underneath

Each one carries its own evidence, scope and caveats. Expand any of them to reach the studies.

Years dried out, credibly. A century traces to a leg twitching in a museum drawer.

Well supported

Good evidence backs this, though some details remain open.

Controlled rehydration of dated herbarium moss samples yields revival from material up to approximately nine years old, with survival declining steeply as storage time increases and no revival from substantially older material. The frequently cited figure of survival exceeding a century traces to a single unreliable report of movement observed in a museum specimen, which was not a demonstration of revival and was not presented as one. Long-term anhydrobiotic survival is therefore progressive decay rather than suspended animation.

Who this applies to
anhydrobiotic micrometazoans in dried moss, from dated collections
Studied in
Tardigrada, Rotifera, Nematoda

You may have heard

“Tardigrades can survive dried out for over a century”

The figure descends from somebody observing a leg move in a museum specimen — which is not revival, and was not reported as revival. Tested against material of documented age, credible survival runs to years and in some cases approaching a decade, which is extraordinary for a millimetre-long animal spending it as dust. The more interesting finding underneath is that survival *declines* with time in the tun: it is not a pause button but a very slow leak.

Why we rate it this way, and what the caveats are
Well supportedModerate confidence

Herbarium material anchors survival times to a documented date rather than an estimate, which is the right design. Absence of revival cannot fully distinguish death from failure to rehydrate under the conditions used, and later work has extended credible times somewhat.

How far it can be extended

The same pattern of declining survival with storage time was found across tardigrades, rotifers and nematodes in the same samples.

Caveats

  • Herbarium storage conditions were not controlled for this purpose and vary between samples.
  • Failure to revive cannot be fully distinguished from failure to rehydrate under the conditions used.
  • Species identity in old moss samples is frequently uncertain.

Still unanswered

  • What accumulates during the tun state to make revival progressively less likely — oxidative damage, protein degradation, or something else?

Last reviewed 2026-08-11

The evidence (2 studies)

Go deeper

Tardigrade

It survives the vacuum of space by turning into glass — and dies at the temperature of a warm bath when it is awake.

Last reviewed 2026-08-11