Water Bear aka Moss Piglet

Fast Facts

Latin name: Tardigrade

Notable feature: They look like chubby bears with eight legs but move very slowly

Conservation Status: Not Evaluated

Where in the UK: Pretty much anywhere, but most obviously in damp environments, i.e. amongst moss and lichens


Tardigrades (aka Water Bear/Moss Piglet) are microscopic eight-legged creatures, measuring 0.1mm to 1.2mm long. They look like chubby bears but move very slowly – this is where the name Tardigrade comes from, it means ‘slow walker’.

When viewed under the microscope Tardigrades crawl around in a clumsy manner making them a popular subject to study.  Considered aquatic because they require a thin layer of water around their bodies to prevent dehydration, they’ve also been observed in a variety of environments, from the deep sea to sand dunes. Freshwater mosses and lichens are their preferred habitat, hence one of their nicknames, Moss Piglet.

Despite looking cute and squishy, Tardigrades are covered in a tough cuticle (very similar to the exoskeletons of grasshoppers, praying mantises, and other insects to which they are related). In order to grow Tardigrades have to shed their cuticles. Each of their eight legs has a foot and each foot has four to six claws; these help them hold on to plant matter.

Most Tardigrades use a sharp straw-like mouthpiece (called a bucco pharyngeal apparatus) this enables them to suck nutrients from plants and micro-organisms. Some seawater Tardigrades are carnivorous and eat tiny animals such as nematodes and rotifers.

Tardigrades have the ability to perform cryptobiosis – this is when a creature can survive difficult environmental conditions, such as freezing or lack of oxygen for a very long time. Tardigrades can dry out and survive for years without water. When water becomes available they are able to rehydrate and come back to life, all in a matter of minutes!  Dried out Tardigrades (known as a tun) are so small and light, the wind will often pick them up like grains of dust and blow them for thousands of miles.

Tardigrades are hardy creatures and are able to withstand extreme pressure (6000 atmospheres) and temperatures (-272oC to 151oC). The little creatures were put to the test in September 2007 when Ingermar Jonsson of Sweden’s Kristianstad University and colleagues launched two species of dried-up Tardigrades into space.

After 10 days in space – with no air, intense rays from the sun and no water the Tardigrades were rehydrated and a handful managed to survive! They are the first animals on earth known to be able to survive the harsh conditions of space.

Around 1,300 species of Tardigrades are found worldwide.

    • Size: 0.1mm-1.2mm long.
    • Life span:  Varies depending on species and can be 3–4 months up to 2 years when they have enough food and water (not counting the times they may be dormant).
    • Diet: Tardigrades eat liquids to survive; sucking the juices from algae, lichens and moss. Some species are carnivores and will even eat other Tardigrades.
    • Reproduction: Depending on the species, Tardigrades may reproduce asexually or sexually.  Female Tardigrades lay eggs which take around 40 days to hatch.  They can take as long as 90 days, if they’ve been in a desiccated state.
    • When to see:  Because of their size you will need a microscope to be able to see a Tardigrade (alternatively check out one of the many scientists on Social Media who share images and videos of their work).
    • Population Trend:  Unknown
    • Threats: Tardigrades have been described as pretty much indestructible, surviving in a state of “tun” for decades, when conditions aren’t right for them.
    • Fun Fact: They are the first animals on earth known to be able to survive the harsh conditions of space.

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