These slow-moving, microscopic invertebrates (soft bodies) of the phylum Tardigrada are called “water bears”, also known as Tardigrades or moss piglets. They have four body segments and eight legs. They are related to the arthropods (which includes spiders, insects, and crustaceans) and Onychophora (velvet worms), and are usually referred to as a “lesser known taxa” of invertebrates. They are found surviving primarily in water or damp moss.

Photos credit: Willow Gabriel, Goldstein Lab

An European Space Agency (ESA)’s experiment has shown that these invertebrates can survive in the vacuum of space and they are the first animals known to be able to survive the harsh combination of low pressure and intense radiation found in space, and even they’re still found alive with intense pressure, huge doses of radiation, and years of being dried out. In fact, they are the greatest survivors in the nature as they have long been known as the virtual indestructibility animals ever survived on Earth.

Photo credit: Ralph O Schill

Water bears, similar to the picture you see above, were brought to low-Earth orbit in an ESA satellite. With the aim to further test their hardiness, Ingemar Jönsson of Sweden’s Kristianstad University and colleagues launched two species of dried-up Tardigrades from Kazakhstan in September 2007 aboard ESA’s FOTON-M3 mission, which carried a variety of experimental payloads. The satellite then returned to Earth after these water bears were exposed to space for 10 days. They were later retrieved and rehydrated to test how they reacted to the vacuum (airless) conditions in the space, oxygen deprivation, bombardment and other radiations by ultraviolet, the ultraviolet radiation from the sun, and charged particles from the space called cosmic rays as well. The outcome of this test was published in the journal of Current Biology, a year after the launch of this mission. The result tells us that the vacuum has little effect on these creatures, but the ultraviolet radiation which can damage DNA and cellular material did take the toll.

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You won’t hear these organisms crying for help in the space. Not only they can survive the vacuum of the space, but also they’re strong enough to venture a trip via that icy, intense radiation and even the onslaught of the unfiltered rays of the sun. Remarkably, a number of these individuals have found to be able to survive through a combination of the space which will definitely have their DNA destroyed as well as to have their bodies dried-up. This is coupling with the solar radiation which might have fried them completely. Nevertheless, these creatures have shown to successfully conquer the most extreme conditions that exist in an intense radiation, high pressure and the vacuum of the space.

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“No animal has survived open space before,” says developmental biologist Bob Goldstein of the University of North Carolina at Chapel Hill, who was not affiliated with the study. “The finding that animals survived rehydration after 10 days in open space – and then produced viable embryos as well – is really remarkable.”

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This ability to survive in extreme conditions “might be important when we consider the habitability of other bodies in our solar system or beyond,” says astrobiologist Gerda Horneck of the German Aerospace Center. But the results say little about how the animals might develop and reproduce in harsh environments, Horneck says.

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Before this discovery, according to the academic reports, only lichens and bacteria have been identified to be able to withstand the combined assault of space and solar radiation. Up to now, the researchers are not sure how exactly these water bears managed to survive in these extremely harsh conditions.

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In 1773, an aquatic zoologist, Johann August Ephraim Goeze came to discover these tiny and segmented animals and they are later given the name as Tardigrada, which means “slow stepper.” Three years later, they were discovered by the Italian biologist, Lazzaro Spallanzani. Three pictures above show the early illustrations of the water bears (Eurardigrade) by Andrew Pritchard. They simply look like cute and lovely animals for you to consider having them as pets.

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Tardigrades are short in general, with their body length ranges from 0.05mm to 1.2mm.

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Water Bears have four pairs of legs with four to eight claws on each. They are bilaterally symmetrical, plump and segmented organisms. Their stout bodies appear in a shape of cylinder. There are sharp pointy objects in their mouths called styles, which help them to cut into moss leaves or algae (their main food sources). After that, they will suck the juices from the plant. They also feed on the fluids from other plant cells, animal cells, and bacteria. They are prey to nematodes, amoebas, and other Tardigrades.

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Tardigrades reproduce either asexually (parthenogenesis) or sexually. Their females are found more in amount than males and they are also found slightly larger than males. Females lay eggs in a shed exoskeleton after mating. They molt just like crayfish and insects. Before the young can become an adult, they must molt (shed their exoskeletons) several times. They can be in different color, including bluish, yellowish-brown, reddish, brown and gray. Their color difference is very much depending on their species.

Photo credit: John Conrad

It is documented that there are over 900 species of these water bears distributed all over the world, with their geographical distributions ranges from the Himalayan Mountains primarily at the elevations of over 6,000 m to the deep ocean of 4,000m beneath the sea level. They can often be found by soaking a piece of moss in spring water. Picture above shows the Water Bear (Echiniscoides sigismundi) with its body length of 0.3 mm which was found on green algae. It was taken from the cement wall of the harbour basin of the city of Lisbon, Portugal.

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Water bears are frequently found living on lichens, mosses, liverworts and even on various types of sediments. A few species of them live on plants in fresh water. The picture above shows how this water bear is moving slowly in the moss water.

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These creatures are indeed amazing animals found on Earth so far! Where on earth could you find any animals who can sustain the most extreme conditions like them? No matter how you treat these creatures, whether they are put in the open space and radiation for as long as 200 years; or whether they are placed in hot sea vents, these 1mm-long creatures are still energetic and they are as active as a child. In short, they are amazing animals that are found to be survived at temperatures close to absolute zero, temperatures as high as 151°C (303 °F), 1,000 times more radiation than any other animals, and nearly a decade without water.

Photos credit: Ian M.Martin

Here are some photographic evidences to show that they are the greatest survivors of the nature, as they will never defeat to any extreme conditions that they might have to face in their life. (First row, left photo: extreme dehydration; first row, right photo: in the vacuum; second row, left photos: extreme heat; and second row, right photos: extreme radiation (A gray is approximately 5,000 chest x-rays, in which 10 to 20 rays can easily kill most animals and a human. These creatures are found to be able to survive easily at 5,700 grays of radiation. They’re simply amazing!) Now, come challenging them! They won’t confess to death even you boil them, freeze them or put them into any harsh conditions. They are such tough guys that you could never beat them down!