Meet the Tardigrade, the toughest animal on the planet

These tiny, roly-poly creatures may seem vulnerable, but they have a secret that can allow them to live indefinitely.

Tardigrades, also known as ‘water bears’ or ‘moss piglets’ are tiny plump caterpillar-like creatures that live in tree bark, moss, almost anywhere there is water. The biggest would be one-and-a-half millimeter long, the smallest, barely half a millimeter. Seen on a microscope, they are usually translucent because of their water content.

Water bears have four pairs of chubby legs that have claws at each end, earning them the nickname. Plus, they move like bears too. The name “Tardigrade” comes from the Latin “slow walker”. They feed on plant matter or tiny invertebrates.

It is hard to imagine Tardigrades earning the title of the world’s toughest animal: they are small, generally harmless, minding their own business. But beneath the cute appearance is an extraordinary ability.

Normally they live up to six months or more. The female shed its skin, lays the eggs inside the skin and the male then fertilizes them. The baby Tardigrades hatch in about two weeks, being born already having the complete number of cells they will ever have in their lives. They grow by making their cells expand (hypertrophy), not by cell division.

And that is usually all that happens in the water bear life cycle. Except for their ability to endure. When hard times come — say in very cold or hot temperature, or when there is very little water, Tardigrades go into a state of suspended animation called “cryptobiosis” (“hidden life”). They retract their legs, lose 99% of the water in their bodies and shrink into a dry ball called a “tun.” And they can keep on doing this indefinitely.

In the tun state, Tardigrades can survive very high or low temperatures, very high or low pressure, extreme dehydration, radiation, and toxins. Imagine these kinds of:

• Temperature – hotter than boiling water (up to 151 °C or 424 K), or colder than ice (down to -200 °C  or 73 K) — even surviving a few minutes exposure to temperatures 1 degree above absolute zero.

• Pressure – from the lowest pressure vacuum of space (at least for ten days, all the while being bombarded by UV radiation — they laid healthy eggs back on earth) going up to 6,000 atmospheres (1,200 times the normal atmospheric pressure — six times greater than the pressure in the deepest ocean floor).

• Dehydration – up to 10 years with just 1 to 3 % water content, even at freezing temperatures.

• Radiation – can withstand doses of destructive gamma-rays and heavy ions that are a thousand times the amount fatal to humans.

•  Toxins – heavy pollution, but this has yet to be verified.

It is no surprise then, that Tardigrades are found almost everywhere on the planet — from the high Himalayas (where Mt. Everest is) to deep sea levels (where you can sink Mt. Everest with plenty of room to spare); and from the polar regions to the equator.

Seeing they are found almost everywhere on the planet, and can even survive outer space, some scientists think it is possible water bears could have come from places other than the earth.

The answer to that is unknown at the moment. One thing’s for sure: the Tardigrades’ toughness is out of this world.

 Tardigrade Video