The Toughest Animal on the Planet

Imagine the toughest animal on the planet. This creature can survive temperatures from -272 to 100 degrees Celcius (Xiaochen and Lizhi 2005, Hengherr et al. 2009). They can also survive radiation a thousand times higher than would be lethal to humans (Horikawa et al. 2008).

The toughest animal on the planet?

The tardigrade or the water bear.

But let’s back up for a second. What in the world is a Tarigrade? Besides being cute and cuddly, water bears belong to thelesser-known phylum of invertebrate animals; the Tardigrada. The first tardigrades were discovered in 1773 and they live in marine, fresh water, and semiaquatic terrestrial environments. Their ability to withstand those conditions can enter a kind of hibernation known as “cryptobiosis” a death-like state during which the tardigrade undergoes an almost complete loss of body water.

Tardigrades are the toughest animals on the planet, but they may also be the toughest animals in the universe. Yes, these brave explorers have been sent into vacuum of space, surviving freezing temperatures, weightlessness and extreme dehydration (Jönson et al. 2008). If you thought that wasn’t enough they also had to deal with extremely high levels of cosmic rays and solar radiation (Ralph 2010). It is interesting to note that the space vacuum and cosmic radiation did not affect their survival or reproduction at all. They must be protecting their cells from expected damage of the extremely dehydration impact of space vacuum or perhaps could repair damage that arise in some way. Some people believe they may have actually come from space: (

Previous only unicellular organisms and cultivated cells of multicellular organisms had been exposed to space environments. Tardigrades are multicellular heterotrophic organisms with brain, nerves, digestive system allows the conduction of experiments with animals characterized by a high level of hierarchical biological complexity and by complete physiological processes.The use of tardigrades as a model system in space research understanding how tardigrades withstand extreme stresses, but also for the development of novel technologies in the field of space protect as we humans move farther our own solar system and beyond.



L. Xiaochen, W. Lizhi (2005). Effect of thermal acclimation on preferred temperature, avoidance temperature and lethal thermal maximum of Macrobiotus harmsworthi Murray (Tardigrada, Macrobiotidae). Journal of Thermal Biology, 30 (6), pp 443-448.

S. Hengherr, M. R. Worland, A. Reuner, F. Brümmer, R. O. Schill (2009). High-temperature tolerance in anhydrobiotic tardigrades is limited by glass transition. Physiol Biochem Zool, 82 (6), pp 749-755.

D. D. Horikawa, T. Sakashita, C. Katagiri, M. Watanabe, T. Kikawada, Y. Nakahara, N. Hamada, S. Wada, T. Funayama, S. Higashi, Y. Kobayashi, T. Okuda, M. Kuwabara (2006). Radiation tolerance in the tardigrade Milnesium tardigradum. Radiation Biology, 82 (12), pp 843-848.

K. I. Jönson, E. Rabbow, R. O. Schill, M. Harms Ringdahi and P. Rettberg (2008). Tardigrades survive exposure to space in low Earth orbit. Current Biology, 18 (17), pp 729- R731.

O. S. Ralph (2010). Anhydrobiotic Abilities of Tardigrades. Dormancy and Resistance in Harsh Environments, 21, pp 133-146.

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