Water bears, also known as tardigrades, are known for being almost indestructible on earth. These microscopic creatures can survive intense pressures, huge doses of radiation, extremes of hot and cold temperatures and years of being dried out. They can be found in moist environments throughout the world, in places as diverse as hot springs, under layers of ice, the Himalayas, ocean waters, on stone walls, and in soils.
Tardigrades were discovered in1773 in Germany by J.A.E. Goeze, a zoologist and pastor, who said of them, “Strange is this little animal because of its exceptional and strange morphology and because it closely resembles a bear en miniature. That is the reason why I decided to call it little water bear. “They have their own phylum, Tardigrada, because they fit in with no other group of animals on the earth. The word tardgrada i comes from the Latin words tardus ( slow ) and gradu ( step ). The literal meaning is “slow- stepper ” and can be appreciated when watching them move about, somewhat akin to a lumbering bear.
Although soft and squishy, they are anything but softies when it comes to extreme environmental conditions. They can survive temperature extremes from – 328° F to + 303° f and pressure extremes from a vacuum to the high pressures in the deepest ocean trenches. They are able to survive radiation levels 1,000 times above that which would kill humans. Water bears can also survive the loss of 99% of the water content of their bodies.
These creatures have the ability to survive the most extreme conditions that would kill any other creatures, even 10 years without water. They may enter a state of cryptobiosis where metabolism is lowered to less than 0.01% of normal, and water content can drop to 1% of normal. A water bear is known as a “ tun “ while in this state of suspended animation, and can survive like this for ten or more years. Some water bears survived on a dessicated piece of moss in a museum for 120 years, becoming active after scientists added water to the moss. While in this dry state they are able to resist storage in liquid nitrogen, contact with mineral acids and organic solvents, radioactive radiation and boiling water. All it needs is a droplet of water and it is able to return to normal activity.
One scientist has compared the appearance of water bears to gummy bears due to their bright orange, green or red bodies and the similar texture of their bodies. A Tardigrada‘s body is barrel-shaped and has four pairs of stubby legs. Legs are without joints and the feet have four to eight claws apiece which enable it to move along and grasp the moss or lichens they are feeding on. Its exoskeleton contains chitin and is molted periodically throughout its life span, which normally ranges from 3- 30 months. Its tubular mouth has stylets which are used to pierce plant cells or the cells of other invertebrates on which it feeds. Often they are seen in postures that really do resemble those of bears, even as they swim through liquids.
To find water bears, look on moss or lichens, even on stone walls or bricks. If the material is dried up, moisten with spring water. Water bear, if present, usually become active within twenty minutes of adding water. Use a microscope and add a drop of the moistened material to a slide. Sometimes water bears are found in soils, so that is another place to look. They are small- 0.1- 1.5 mm. the largest being about the size of the three small dots found on a dime between the neck of Franklin D. Roosevelt and the date the coin was minted.
Scientists have reported finding water bears on mountain tops, in hot springs, under layers of solid ice and in the sediments of oceans. Many species can be found in the less extreme environs of ponds, meadows, lakes and back yards. Some have even been found on roofs. While most common in moist areas, they are able to stay active as long as they maintain just a thin film of water around their bodies.
Certain species of Tardegrada were found to be resistant to the effects of space when used in experiments by NASA. During the flight mission the tardigrades molted, and females laid eggs. Several of the eggs hatched with the newborns exhibiting normal morphology and behavior. Neither the microgravity nor the radiation found in space had any effect on the survival capability or the integrity of the DNA of active tardigrades.
The water bears ( or moss piglets as they are sometimes called ) are singular specimens in the world of Zoology. No other animals show such a profound ability to survive conditions that cover as wide a spectrum of environmental extremes, while remaining virtually unknown to most of the people living all around them.
Sources: NASA Science NASA News
Carleton College – Microbial Life Education Resources