Tardigrade, most resilient creature on earth. The Earth is only planet in solar system or perhaps in galaxy that sustains life and conditions necessary for life. Humans are indestructible at this point unless we involve ourselves in affairs such as war or climate change. What if you are told that there is toughest creature on earth that has survived harsh conditions and is still alive. 

Tardigrade, the most resilient creature on the earth

So just prepare yourself for Tardigrade, the most resilient creature on the earth or perhaps in the whole galaxy. It is considered that the Tardigrade first appeared about 600 million years ago. Also known as Water Bears and Moss Piglets, they are micro-animals, segmented, have eight legs and are water dwelling.

They were first discovered by Germen Zoologist Johann August in 1773 and the name Tardigrade was suggested by Lazaro Saplanzanni, meaning “slow stepper”. Talking about the size of the animal, it is really small and cannot be seen with the naked eye.


Common house flies are about 6-7mm long, ticks being about 3mm, mosquitoes are about 2mm (about the size of a pinhole) while the biggest tardigrade is about 0.5mm or about 1/50 of an inch. Tardigrades can survive any condition and any habitat.

They have been found almost everywhere, from toughest rocks and mountains to the deep seas and oceans and in the mud volcanoes, tropical rainforests and even in Antarctic. They have prominent sexes, males and females which reproduce to form offsprings.

The shells are hard and can survive transportation. The newborn are fully grown, they do not produce new cells after they are born, but the cells forming their bodies expand, a process known as hypertrophy. In this process the tardigrades molt and leave behind their outer layer, much like a snake sheds its outer layer.


Knowing about the classification of these animals, they are invertebrates, regarded as the closest relative of arthropods and belong to the phylum Tardigrada. The phylum Tardigrada is further sub-divided into two classes: Heterotardigrada and Eutardigrada, each having two classes.

The whole phylum consist of about 1200 species. After their discovery, August first named them Kleiner Wassarbar, meaning “little water bear”, as obvious from their appearance. They look like bear and are slow-moving. However, they were re-named in 1776 by Lazaro as Tardigradum which means “Slow Walker”.

They are mostly found on lichens and mosses, however, they dwell a variety of places such as sand dunes, mountains, oceans and even mud volcanoes. Scientists have identified these creatures in the boiling hot springs and even in the deep ice stones of Himalayan mountain range. One of the easy way to find a tardigrade is by soaking a piece of moss in water. But they are not visible through naked eye and require microscopic identification.

Survival of Tardigrade

Question arises that how this animal has survived extinction despite of the harsh and challenging conditions. Here are some of the facts. Experiments reveal that this animal can survive temperature as low as -3280F and as high as 3000F.

It can withstand a pressure as high as 6000 times that of the atmospheric pressure and can tolerate the damaging effects of radiation that would otherwise cause mutations in the human DNA. In 2007, a group of European researchers carried out an experiment on this organism.

They first dehydrated the animal, carried it to the outer space and exposed it to the solar radiations for about 10 days, brought back, rehydrated and allowed the animal to grow in the normal conditions.

It was observed that the members which were not exposed to the radiations survived and produced viable off-springs while the members which were exposed to the harmful rays came back to life and produced normal off-springs like their parents and didn’t show any mutation.

How does a tardigrade survive dehydration? Well, after encountering unfavorable conditions, tardigrade goes into a dehydrated state and curl up upon itself, forming a dead ball called Tun, decreases its metabolic activity and produces a special sugar that forms a gel-like medium called trehalose which provide a medium to its organelles and other cellular structures to be suspended in it.

The longest time that a tardigrade has survived dehydration is about 10 years. When the dehydrated form is placed in water, it absorbs water and comes back to living state in about few hours.


The tardigrades are capable of other types of transformations as well. For example if the oxygen level of water falls below the normal, they stretch out their bodies into relaxed state. In this way their body and muscles are able to absorb maximum water and extract oxygen.  

The bodies of tardigrades are large barrel-shaped consisting of a head, three segments (each having one pair of legs) and a caudal segment with the last pair of legs. The legs do not have joints and each leg have about four to eight claws.

The first three pair of legs are directed downwards while the fourth pair is directed towards the back. The body is covered by cuticle and protein which can be molted from time to time. They do not have well developed circulatory and respiratory systems and the body cavity found is called haemocoel.


Tardigrades mainly feed on plant cells, algae and small invertebrates. That are cut down into smaller chunks by the stylets present in their mouth. Mouth opens into a pharynx which in turn opens into a small esophagus and then into a large intestine. That occupies most of the space in the body and thus is the main site of digestion. The intestine opens into anus through a short rectum.

Do tardigrades have brain? The answer to this question is simply yes. Tardigrades have a brain which consist of three lobes which are further composed of clusters of neurons. The brain is attached to a large ganglion (Cluster or group of nerve cells) below esophagus. From there, a nerve cord arises and runs throughout the length of the body.

Tardigrades that live in aquatic environment feed on other species such as nematodes, small invertebrates, plants and even bacteria. Despite of their diverse habitat, their ecological importance, development and genome is not yet clearly understood by biologists. But it’s a fact that Tardigrades are super-amazing.

By Razmia Sabahat Butt

I'm a student of BS Applied Biosciences at NUST, Islamabad.