This is a repost from my previous blog, from November, 20006, the second of 2 parts. First part here.
I first read about water bears, or tardigrades, a year ago, in "Nature in Miniature" by Richard Headstrom. (1968) Unfortunately, he misled me: he said that "the only way to find it is to add a little water to the sediment of a rain gutter or the mud from a pond and examine it with a microscope." So I've been looking all along in the wrong places, and not realizing I could use a hand lens. I found it, finally, in moss, as I wrote a few days ago. (2006)
The water bear, probably so named (in 1773) because it looks somewhat like a miniature bear, is a tiny animal, barely growing to 1.2 mm. Enough to be seen with the naked eye in a good light, just. Add to that, that it is transparent, and the light has to be falling from the right angle. But still, well worth the look.
Basic body structure: 5 segments, 8 legs, each with tiny "claws" that look something like a mole's digging feet. Two eyes, small and almost invisible, even under a 60x microscope. A round mouth/snout like the business end of a nose-hair clipper. Not much else; it's a very simple animalcule.
They eat bits of detritus that they find in their placid amble; some are vegetarian, some meat-eaters. Some reproduce asexually, but not all. They live everywhere on earth, wherever they find water, fresh or salt.
And they are slow-moving. That's why they're called the "tardigrades", or "slow steppers". But determined enough to travel a fair distance nontheless. Stubborn little beasties.
More than stubborn: Headstrom calls it "one of the toughest animals we may ever expect to find."
They need water to be active. But give them a spell of dry weather, and they shrivel up into a "grain of powder". (It doesn't matter what stage of life they are at, either; they go into cryptobiosis, "hidden life" at almost any stage.) (Added, 2008) Leave them that way for years. Wet them down and wait a few hours, and they swell up and walk off as if nothing had happened.
Freeze them. No problem. They live happily in Antartica. They can survive down to -272 degrees Celsius. Try that yourself!
Boil them. Not to worry; boiling water only reaches 100 degrees C; the water bear can tolerate 150.
Deprive them of oxygen, douse them with salty brine, boiling alcohol. Radiate them with X-rays. Squish them with hundreds of atmospheres of pressure (6000 according to 'New Scientist', 31 October 1998, p. 26. From here.) Store them in a vacuum. Why not? If the treatment doesn't suit them, they roll themselves up in a little ball and go into stasis, like the colonists in sci-fi novels aboard their inter-galactic ships. A "tun", they call this, like a casket of ale. No ale in this tun, though; just a special sugar that takes the place of water in their cells.
Give them water and air, and they pop right back. From Carleton U., I learned that "Live tardigrades have been regenerated from dried moss kept in a museum for over 100 years!" It has been speculated that they could survive a trip in space.
And the little beastie I found the other day looked so small and fragile, I felt as if (knowing that I was not, but still -- he was so tiny!) I were treating him too roughly as I sucked him up into the eyedropper and dumped him on another plate. Deceptive, as well as tough.
Other resources: Animal Diversity Web , Carleton U., Microbial Life Educational Resources . Sandra Porter has more. And so does Christopher, as I noted earlier.