Here’s why they’re called water bears.
Tardigrades are microscopic, water-dwelling invertebrates with eight legs that seem to have a bear-like appearance and gait and tend to cling to moss or lichen; characteristics that have given them the nicknames water bears or moss piglets. Although they breathe through their skin and therefore lack respiratory organs and a circulatory system, the anatomy of water bears is quite complex.
Like a wrinkled caterpillar.
The water bear’s body is covered by a chitinous layer that is regularly moulted, similar to insects. Females and males occur in most species and many have complicated courtship behaviour and mating rituals. Depending on where they live, water bears can be strongly pigmented from orange and bright red to olive green for those living on mosses and lichens – often with a density of up to 25,000 animals per liter!
Yup, this is where they live – on pillow moss or Grimmia pulvinata.
Though tiny at only 0.1 mm to 1.5 mm, tardigrades are everywhere – from the icy climates of Antarctica to the sweltering heat of the equator; the high altitudes of the Himalayas (6,000 m/19,800 ft and above) to the deep sea (below 4,000 m/13,200 ft). More than 1,000 species of tardigrades have been identified since their discovery by German zoologist Johann August Ephraim Goeze in 1773 and there’s even an International Tardigrada Symposium held every three years.
Ain’t he cute – kind of potato like, don’t you think?
Now the big question is, what do these hardy animals eat? Most of them live off the cell content of bacteria, algae and mosses that they suck out. Three marine species are known to parasitize sea cucumbers, barnacles and aquatic invertebrates. A few species are carnivores and feed on microscopic wheel animals, roundworms and even each other!
They’re lovingly also called tardies by those studying them.
In September 2007, the European Space Agency even took two species of tardigrades into Space, about 160 miles up. Some water bears were exposed to the vacuum of space only, others to ultraviolet radiation as well – about 1,000 times more than on Earth. All not only survived unharmed but even procreated and laid eggs that survived normally. Thus, they join the few species of lichens and bacteria as the only ones to survive the vacuum and solar radiation of Space unprotected.
Tardigrade eggs in exoskeleton.
The more extreme the environment, the better the water bear adapts. The facts are just so amazing and unbelievable that we have to sum them up again: Tardigrades can withstand extreme temperatures of -273°C (-523 °F), close to absolute zero, temperatures as high as 151 °C (303 °F), 1,000 times more radiation than any other animal or human and go almost a decade without water! On top of that, throw them into a vacuum, organic solvents such as 96% alcohol or ether, or even liquid helium and they’ll be fine.
Looks like a water bear in 2D – only 0.7 mm long.
The secret to the tardigrade’s success? Water bears are not only able to reach a state where their metabolism has ceased entirely but to maintain this state for years and at any stage of their life cycle! The image below shows the Arctic, moss-dwelling water bear Adorybiotus coronifer in a dried and extremely cold-tolerant state.