Tardigrades: Unraveling the Mysteries of the Little Water Bears

Tardigrades are microscopic animals found to withstand extreme conditions that would kill even the most resilient animals today, including humans, but how do they do it?

April 2019, the first privately funded lunar mission, the Israeli Beresheet probe, crashed on the Mare Senitatis-- a plain of basaltic rocks formed in a volcanic eruption a billion years ago, after a last-minute instrument failure.

The Beresheet was carrying a payload of tardigrades, famed among biologists for their impressive resilience and ability to survive extreme conditions. The inactive tardigrades are believed to have survived the crash that plummeted the probe into the lunar surface at 500 kilometers per hour.

The Discovery of the Little Water Bears

Tardigrades that resemble a cross between a microscopic caterpillar and woodlouse aren't as difficult to find as one would think.

If you went out on a damp day and found a wet patch of moss or lichen, there's a high chance that you'd find tardigrades swimming about in the water using a microscope.

Despite their microscopic size, tardigrades have been known for ages. First described in 1773 by German naturalist Johann August Ephraim Goeze. He named the bizarre creatures "little water bears" due to the way they walked.

The name tardigrade that loosely translates to "slow stepper," was bestowed a few years later by Lazzaro Spallanzani, an Italian priest-turned-biologist in his book Opuscoli di Fisica animale e vegetabile or Booklet of Animal and Vegetable Physics.

ALSO READ: MBL Researchers Imaged First Body Plan Moments in the Embryo

Unraveling the Mysteries of the Tardigrade

Despite their minuscule size, tardigrades are complex animals. Nadja Mobjerg from the University of Copenhagen, Denmark, explains that the little water bears are built by roughly 1,000 cells, as complex as cockroaches and fruit flies, including mouthparts used to puncture algal cells other food sources.

Lorena Rebecchi from the University of Modena explains that tardigrades have variable reproductive strategies, with some as males and female, while others are hermaphrodites, and others reproducing parthenogenesis or "virgin births."

On the other hand, the infamy of the tardigrades is due to their extraordinary resilience. Thomas Boothby from the University of Wyoming lists threats that tardigrades can endure: the little water bears can survive drying out and frozen down a degree above absolute zero--temperatures at which molecular motion stops.

In their dry state, tardigrades can be heated up past the boiling point of water and can survive thousands of times more radiation than humans. In addition, tardigrades are the only animals known to survive prolonged exposures to the vacuums of outer space.

Researchers theorize that tardigrades first evolved their resilience when the need to survive on dry land arose. Their strategy was to enter a dormant state where cells and organs would be packed away by protective chemicals.

Inadvertently, this process also made the little water bears resilient to other stressors such as extreme cold and radiation because the ability to temporarily halt all biological processes works just like the said situations.

If the theory is correct, tardigrades' near-invincibility was an accident that could help preserve themselves in outer space.