Tardigrade (Water Bear) (phylum Tardigrada)

InvertebrateMicro-animalExtremophile

Overview

Tardigrades — affectionately known as “water bears” or “moss piglets” — are microscopic animals that form their own phylum (Tardigrada). Usually well under a millimetre long, they have plump, segmented bodies and eight stubby legs ending in tiny claws, and they trundle along under the microscope with a bear-like gait. Despite being so small and obscure, they are among the most famous animals in science for one astonishing reason: they are nearly indestructible.

Tardigrades can endure conditions that would kill almost any other creature — from boiling heat and near-absolute-zero cold to crushing pressure, intense radiation, being completely dried out, and even exposure to the vacuum of outer space.

Note: there are over a thousand tardigrade species with differing tolerances; details here cover them broadly. Images of tardigrades are microscope views, since the animals are too small to see with the naked eye.

Habitat & Range

Tardigrades live almost everywhere on Earth — from the deep sea and high mountains to tropical forests, polar ice, and hot springs. Most familiar are the ones living in the thin film of water on mosses, lichens, and leaf litter, and in soil and freshwater sediment. Wherever there is at least a little moisture, tardigrades are likely present, often in large numbers.

Diet

Most tardigrades feed by piercing the cells of plants, algae, mosses, or other tiny organisms with sharp mouthparts and sucking out the contents. Some are predators that eat other tiny animals, including other tardigrades and microscopic roundworms. They need a film of water around them to be active and to feed.

Behavior

The tardigrade's superpower is a survival trick called cryptobiosis. When its environment dries out (or becomes otherwise hostile), a tardigrade pulls in its legs, loses almost all its body water, and curls into a shrivelled, dormant ball called a “tun.” In this state its metabolism essentially stops, and it can persist for years — possibly decades — until water returns and revives it. In tun form, tardigrades have survived extreme heat and cold, high doses of radiation, immense pressure, and exposure to the vacuum and radiation of space in experiments. When conditions improve, they rehydrate and carry on as if nothing happened.

Human Interaction & Conservation

Tardigrades are harmless and have become beloved science icons, studied intensely for how they survive drying out and radiation — research with possible applications in preserving cells, vaccines, and biological materials, and in understanding life's limits. They are not of conservation concern as a group. Their toughness has even made them a fixture of popular culture. Consult authoritative sources for details.

More photos of the tardigrade (water bear)