Tardigrade: Difference between revisions

{{Infobox

| title = Tardigrade

| phylum = Tardigrada

| size = 0.05 to 1.2 mm

| survives = vacuum, radiation, 30 years frozen

| does not survive = 37.8 °C for two days

}}

'''Tardigrades''' are microscopic eight-legged animals also known as water bears.

They survived exposure to open space. They are also killed by a warm afternoon.

== Cryptobiosis ==

A tardigrade under stress expels most of its body water, retracts its legs and contracts into a "tun", replacing lost water with trehalose and protective proteins. In this state its metabolism falls to a fraction of a percent of normal and it can wait.<ref>Ralph O. Schill (ed.), ''Water Bears: The Biology of Tardigrades'' (Springer, 2018).</ref>

In 2007 the European Space Agency's FOTON-M3 mission carried tardigrades on the outside of the spacecraft. Specimens exposed to the vacuum of low Earth orbit, and to the full unfiltered solar ultraviolet spectrum, were rehydrated on return and reproduced normally.<ref>K. Ingemar Jonsson et al., "Tardigrades survive exposure to space in low Earth orbit", ''Current Biology'' 18:17 (2008), pp. R729-R731.</ref>

In 2019 the Israeli lunar lander ''Beresheet'' crashed into the Moon carrying dehydrated tardigrades, so there is now an unknown number of them on the lunar surface in tun state, which is legally and biologically interesting and ethically nobody's finest hour.<ref>"A crashed Israeli lunar lander spilled tardigrades on the Moon", ''Wired'', 5 August 2019.</ref>

== The part the memes leave out ==

An active, hydrated tardigrade is a soft animal with very little tolerance for heat. In a 2020 study, ''Ramazzottius varieornatus'' died at sustained temperatures around 37.8 °C over 48 hours; desiccated specimens did better, but not by as much as their reputation suggests.<ref>Ricardo Cardoso Neves et al., "Thermotolerance experiments on active and desiccated states of ''Ramazzottius varieornatus'' emphasize that tardigrades are sensitive to high temperatures", ''Scientific Reports'' 10 (2020), article 94.</ref>

The animal that shrugged off the vacuum of space can be killed by a hot day in Copenhagen. Its trick is not toughness; it is knowing when to stop being alive for a while, which is a different skill and arguably a better one.

== See also ==

* [[Mantis shrimp]]

* [[Platypus]]

== References ==

{{reflist}}

[[Category:Animals]]

[[Category:True but improbable]]