Water bears: Cute Little Survivors are Everywhere

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Illustration by Adelaide Tyrol

So you think you’re tough surviving a northern New England winter? Well, consider the amazingly resilient “water bears,” creatures that live all around us but that can only be seen through a microscope. They live the world over and can withstand levels of heat and cold, and other environmental extremes, like no other animal.

Water bears live anywhere water is present for at least part of the year. With about 1,000 species currently known, they are found in Antarctica, on Himalaya peaks, in deep ocean water, in parched deserts. Lab experiments have shown them to survive temperatures of 295 degrees Fahrenheit and minus 454 degrees. They survive in extremely acidic solutions, in air without oxygen and in air with toxic gases. They can survive pressures 1,000 times greater than that on Earth’s surface. Tests by astronauts have shown they can live even after intense solar radiation in space.

What are these unusual beings? How do they do it?

Water bears are more technically called tardigrades, a name that comes from the Latin word, tardigradus, meaning “slow moving.” As you might guess, they do move slowly, in a sauntering fashion, in a way that resembles a shambling bear. But they also look like a mite, or maybe a football-shaped worm with legs. Their common name – they’re also called “moss piglets” and “bears of the moss” – suggests an endearing appearance. View them under a lens or check a photo on a Web site, and you’ll probably agree. You might also note that like their distant cousins, arthropods, their bodies are segmented and they have eight legs; unlike anthropods, however, their legs are not segmented, but rather peg-like with claws at the ends that are used for grabbing onto the substrate or, in carnivorous species, capturing prey.

Most species are herbivorous, feeding on mosses, lichens, or other vegetation; but some are scavengers, eating dead matter, and a few are carnivorous, devouring other microscopic animals such as rotifers, nematodes and other tardigrades. In common with more evolved animals, they have a well-developed brain and nervous system, as well as digestive, excretory and muscular systems. Being small and aquatic, they lack respiratory and circulatory systems, but instead breathe though their skins, taking oxygen from water as fluids circulate freely throughout their bodies.

Though dependent on water for their life functions – eating, moving, reproducing, breathing – they have extraordinary powers of survival when water is either absent (through drought or tied up as ice) or too abundant. They may inflate themselves like minute balloons to ride out floods, and they can carry enough of their own oxygen when it is otherwise scarce. In extreme cold or dryness, they can expel almost all of their body water and shrivel into a much-reduced wrinkled form, thereby becoming virtually freeze-proof or drought-proof, as their metabolism ceases. In this state, called cryptobiosis, water bears are, to all intents and purposes, dead. But add water or ameliorate the temperature, and they miraculously spring to life. While they usually live only weeks or months, cryptobiosis allows them to extend their life span tremendously. When scientists at the British Museum in Great Britain recently rehydrated a 120-year-old dried clump of moss, they discovered water bears that, indeed, had returned to life. How they withstood more than a century of dryness remains a mystery.

As far as we know, water bears are neither harmful nor helpful to humans. They just are. Because of their size, they probably won’t ever be in the public eye like birds or mammals or even insects. But as unusual members of our planet, they have gained a dedicated following that seems to be growing. “Tardigrade Clubs” are now popping up to share scientific and other information on Web sites and elsewhere. More scientists are studying them, as well.

One foremost authority, Dr. William Miller of Baker College, Kansas, visited Vermont last year during the Montpelier BioBlitz, a weekend-long intensive survey and celebration of all plants and animals within the city’s boundaries. Miller arrived with his “team” of students, all in green T-shirts, carrying an enormous poster with the image of an especially fetching water bear. Over the course of the weekend, the team discovered a species of water bear new to New England, and Miller enthralled BioBlitz participants with his slide presentations, enthusiasm, the discussions he lead, and the microscope views he offered of living water bears. He won many new water bear fans.

In keeping with that spirit, I offer here a cheer for Team Tardigrade:

Water bears, water bears, fight fight fight,
You may be small, but you’ve got might,
All around the world, in the void of space,
With your tiny legs, you’ll win the race.

Charles W. Johnson of East Montpelier is a former Vermont state naturalist and the author of several books.

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