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Today, I am going hunting for bear in my back yard. Most of my friends are surprised when I tell them this. They say that bear haven’t been seen in this part of the world for many years, and I agree with them - they haven’t. Still, if one knows where to look, one stands a very good chance of finding them.
Of course, I am not talking about the black bear - the native bear in the northeastern United States. Rather, I am looking for the water bear - or tardigrade - as it is known to scientists. Water bears are not even remotely related to other bears and only superficially resemble them. But pound for pound (and it would take many of them to make a pound), they are one of the hardiest, toughest creatures known to science.
Water bears are small, the largest measuring a whopping 1.5 millimeters, or about 1/20th of an inch, long. The weapon of choice when hunting these bears is a microscope.
As the name would imply, water bears live in the water. Some live in salt water, but most are found in freshwater. Because of their size, not much water is needed. The water bears in my back yard can be found in the water trapped between the fronds of mosses and lichens. This water is very important to the water bears because it supplies the oxygen they need to breathe. They don’t have lungs, rather they breathe through their skin, the oxygen in the water diffusing into their body. Therefore, if their home dries out completely, they can not breathe, and they die. But they are only dead until their home regains its moisture, at which time they come alive again!
Water bears are polyextremophiles. An extremophile is an organism that can survive extreme conditions that would kill other organisms. Since water bears can survive a variety of extreme conditions, they are poly-extremophiles.
When water bears encounter extremely dry conditions, they enter a state of cryptobiosis. In this state, all of their life systems shut down. They are essentially dead. But once conditions return to normal, they return to their normal, living selves. In the water bear, this cryptobiotic state is called a tun. Some water bears have been known to exist in this state for 10 years before coming alive again!
When the water bears in my back yard dry out, they can loose over 99 % of the water in their body. Their legs are retracted into the body and they shrivel up, looking nothing like a water bear. Since they have practically no water left in their body, they can also survive very cold temperatures - since there is nothing left to freeze. All of this makes hunting for water bear a winter activity as well as a summer activity. One only needs to find a little dried up moss. Add a little water and observe it under the microscope.* If water bears are present, they will begin to absorb the water, start to fill out to their original shape and begin to move around in their lumbering bear-like way.
Being polyextremophiles, water bears can survive a number of extreme conditions. Other than drying and freezing, some have been shown to be able to withstand very high heat (300℉ for a short time), extremely low pressure ( taken for rides in outer space), excessively high pressure (6,000 atmospheres - over 5 times the pressure at the bottom of the ocean), fatally high radiation (600 times the lethal dose in humans) as well as harmful environmental toxins. Fortunately, none of the water bears in my back yard have to face these challenges.
Water bears are just one part of a community of organisms found in the mosses and lichens in my back yard. They move through their world searching for food, avoiding enemies, looking for a mate - all of the things that the larger bears do. But they do it in such a small scale that most humans never pay them any attention. In fact, most people have no idea that they even exist. They don’t figure in our lives at all.
As I look out my window on a cold winter afternoon, I see patches of mosses and lichens on the rocks and trees in my back yard. Chances are there are water bears by the dozens out there. Chances are they have no idea that we humans even exist. We don’t figure in their lives at all.
Time to change that. Time to go hunting for some water bear. Time to rehydrate some moss and look for them under my microscope. Chances are they will survive this encounter. They seem to be able to survive just about everything else.
* For insdtructions to make a homemade microscope, check out the book, Backyard Biology: Nature Stories and Nature Activities in My Backyard and Beyond.