Water Bears

Nature Notes by Dr. Frank Lang

I like the rustic look of moss and lichen-covered wooden shake and shingle roofs. Mosses and lichens are ecological pioneers, the first plants to invade any bare area: granite outcrop or fresh split shakes. Mosses and lichens put down thin filamentous structures into microscopic cracks and crevices and make them macroscopic. They produce organic acids that soften substrates. They capture windblown debris: dust, pollen, fine soil particles and, sometimes, eggs or spores of other organisms. They change the shake or shingle from a place of temperature and moisture extremes to a cooler, damper, place – a place that wood-rotting fungi might find more hospitable.

I tend to ignore the role they play in shortening the life of a wood shingle roof. I like the mosses and lichens on my roof because I know they are the home of bears. Yes, bears. Not the kind of bears that deposited huge piles of manzanita berries along the irrigation ditch above our house before more houses encroached upon the urban wildland interface, but Tardigrades or water bears. These microscopic, multicellular beasts, half a millimeter or less in length, spend their lives wandering about in moss and lichen forests several centimeters high. Their short, stout, cylindrical bodies with down-turned heads have four pairs of clawed, stumpy legs. Their deliberate, pawing locomotion is most bear-like.

Despite their fearsome claws, used for clinging and climbing, they are mostly herbivorous, although they won’t pass up a juicy nematode or rotifer. They usually pierce the cell wall of moss leaflets and algal cells with sharp pointed mouthparts and suck out the vital juices.

Tardigrades have an unusually large bilobed brain in proportion to their body size. Do they think? Is left brain, right brain a topic of discussion? Most likely not.

Water bears have an amazing facility for suspended animation. No expensive cryonics for Tardigrades, whole body or just the head. When summer comes and mosses dry, water bears contract into a dried, inactive state that can last from four to seven years. How long depends on the amount of stored food in their bodies. When moist conditions return, the animals swell with water, and promptly become active after four minutes to several hours. Under laboratory conditions, animals have been dried and revived ten times or more.

So, if you wake suddenly at night, it might be because of the restless wanderings of water bears on your shake roof. If you have asbestos shingles, it just might be the mating frenzy of your own personal herd of hair follicle mites cavorting around your nose and cheeks. But that’s a topic for a different Nature Note (page 125).

— Dr. Frank Lang   

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