How can a tardigrade survive drying and become active again?

A dried tardigrade can look like a motionless speck, yet some individuals become active again after water returns. This is not ordinary sleep or continued normal life without water. Certain species can enter anhydrobiosis, a drying-induced form of cryptobiosis in which measurable metabolic activity becomes extremely low.

As water is lost, the animal retracts its legs and contracts into a compact form called a tun. Cell chemistry faces serious risks during drying: biological molecules and membranes normally function in a watery environment. Merely becoming smaller does not explain how those components remain capable of working later.

Experiments have identified tardigrade-specific protective proteins as important contributors in studied species. Some are intrinsically disordered, meaning they lack one fixed folded shape under ordinary solution conditions. Drying or concentration changes can make particular proteins associate into fibers, gels or other condensed states. These states can help stabilize biological components, but results for one purified protein are not a complete explanation of an intact animal.

When suitable conditions and water return, protective assemblies can change again and cellular processes can resume. Recovery depends on avoiding irreversible damage, not on repairing an unlimited amount of harm. Species differ in their preparation and molecular protections; sugars and other mechanisms can contribute too. Cryptobiosis is therefore a bounded capacity for surviving particular stresses, not immortality or evidence that every tardigrade withstands every extreme.