Thursday, June 18, 2009

water bears

Have I ever told you about water bears?

If I haven't, I'm really sorry because water bears are amazing. Water Bears (aka Tardigrades = slow walkers ) are microscopic, water-dwelling, segmented animals with eight legs. The biggest adults can reach a body length of 1.5 mm, the smallest a wee 0.1 mm.

Water bears are considered "polyextremophiles", a fancy word that means that they are able to survive in conditions that humans and most other living things would find absolutely dreadful. Some can survive temperatures of -273°C (close to absolute zero), temperatures as high as 303 °F, 1,000 times more radiation than humans, almost a decade without water, and even the vacuum of space.

If you want to try your hand at bear-hunting, you may not have to leave the comfort of your own yard. To find some around your house, your best bet is to look somewhere that is intermittently or permanently damp. The most likely place in a backyard is in clumps of moss or lichen found in damper parts of yards such as the base of trees and walls, in plant pots, and on roofs or gutters.

Put the moss clumps they can be dry when collected in a small shallow dish and thoroughly wet with rainwater so that there's a centimeter of standing water in the dish. Let the moss stand in the water overnight, then remove the excess water from the dish and (this water can be discarded at this point). Use your hands to squeeze the moss clumps out to remove more water from the moss. Collect the squeezed water in a smaller dish or watch glass. Search this dish of water under a stereo microscope at 40x, or the lowest power of your compound microscope. Putting a black background behind your glass might help you see the specimens you've collected. You may need to look awhile in order to find water bears in your sample. Other critters, like worms and rotifers, are likely to be much more abundant. While I have a soft spot for these tiny bears, some of the other creatures are also quite amazing and incredible to watch.

When you're done searching, don't forget to put the moss clump and water back where you found it!

Tardigrade Appreciation Headquarters
Science Friday film about Water Bears

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