Die Hard – meet the tardigrade
I am not sure if the little creatures in the pictures below look uncanny or cute. They kind of remind me of the Hookah-Smoking Caterpillar from “Alice in Wonderland”, so I suppose I consider them to be cute. Tardigrades, also known as water bears or moss piglets (there you go, cute names – these creatures are definitely cute), are a phylum of very small invertebrates. They were first described by the German pastor J.A.E Goeze back in 1773 (who called them “little water bear”) and three years later, Italian biologist Lazzaro Spallanzan named these little fellows Tardigrade, which means “slow stepper”.
Tardigrades have eight legs and the hands present four to eight claws. In terms of size, they can go from 0.05mm to 1.2mm long (0.002 to 0.05 inches), but normally they do not grow over 1mm (0.04 inches).
Water bears can be found pretty much everywhere, from the deep sea to mountaintops, the Antarctic, tropical rain forests, mud volcanoes, etc., but they prefer to live in wet environments, such as the sediments at the bottom of a lake or moist pieces of moss or lichens. These little creatures are amazing and almost indestructible, since they can survive in extreme conditions. A research has found that water bears can endure temperatures as cold as minus 200 Celsius degrees or as high as 150 Celsius. Tardigrades are also able to survive boiling liquids (as the ones in steamy hot springs), enormous amounts of radiation (they can withstand 1,000 times more radiation than any other animal on Earth), high pressure (to up to 6 times the pressure of the deepest part of the ocean, the Mariana trench) and many of them can even survive in space and produce viable offspring. Water bears have been here on Earth for over 500 million years, which means that they even survived five mass extinction events. We usually considerer that cockroaches are the ultimate survivors, but I would say these little water bears are much more resilient.
Scientists discovered that tardigrades are so adaptable to such extreme conditions by enduring a process called cryptobiosis. This process is defined as a state in which metabolic activities are kept in stand-by; this means that tardigrades go into a death-like state. There are several types of cryptobiosis, and our little friends use a few. For example, they can curl into a dehydrated ball called tun and retract their head and legs (anhydrobiosis). When they are brought back to water, they can “resuscitate” within a few hours. In extreme low temperatures, water bears form a special tun that avoids the growth of ice crystals (cryobiosis). In situations that tardigrades are in water with low levels of oxygen, they reduce their metabolic rate, so that their muscles become more relaxed to allow as much water and oxygen to enter their cells (anoxybiosis).
With such remarkable abilities, we can expect that tardigrades will remain alive long after the extinction of mankind and other species. Catastrophic events for man (such as asteroid impacts, nearby supernova blasts, etc.) would mean the end for us, but tardigrades should not be greatly affected and they will remain here, which shows that life does go on.