Tardigrades, often called “water bears” or “moss piglets,” are miniature invertebrates. These eight-legged micro-animals, typically measuring around 0.5 millimeters in length, are barely visible to the unaided eye. Their short, plump bodies and deliberate, lumbering gait inspired their common names. First described in 1773 by German zoologist Johann August Ephraim Goeze, they were later formally named “Tardigrada,” meaning “slow walkers,” by Italian biologist Lazzaro Spallanzani in 1776.
Everyday Habitats
Tardigrades are most commonly found in ordinary, moist environments across the globe. They require a thin film of water around their bodies for active life, enabling gas exchange and preventing desiccation. This explains their prevalence in damp habitats, even though they possess survival mechanisms for dry periods.
Mosses and lichens serve as primary residences for many tardigrade species, clinging to trees, rocks, and even rooftops. These spongy plants retain moisture, creating ideal micro-environments where tardigrades can thrive, sometimes reaching densities of over two million individuals per square meter in moss. Beyond these terrestrial plants, they inhabit freshwater bodies such as lakes, ponds, rivers, and even temporary puddles, often living among sediments and aquatic vegetation. Marine environments also host a diversity of tardigrades, with approximately 150 identified species residing in ocean sediments, intertidal zones, and associated with seaweeds. Damp soil and leaf litter further contribute to their widespread distribution, where densities can reach up to 300,000 per square meter.
Extreme Environments
Tardigrades survive conditions lethal to most other life forms, enabled by a unique state called cryptobiosis. During cryptobiosis, their metabolic activity can slow to less than 0.01% of normal, effectively entering suspended animation. This allows them to endure periods of extreme desiccation (anhydrobiosis), freezing (cryobiosis), lack of oxygen (anoxybiosis), or high salt concentrations (osmobiosis), often by forming a protective, shrunken structure known as a “tun.”
Their survival capabilities span an impressive range of temperatures, from nearly absolute zero at -272°C (-458°F) to scorching heats of 151°C (300°F) for short durations. They can withstand pressures six times greater than those found in the deepest ocean trenches and tolerate thousands of times more radiation than humans, partly due to specialized proteins like Dsup that protect their DNA. Beyond Earth’s surface, tardigrades are the first animals known to survive direct exposure to the vacuum and radiation of outer space, as demonstrated by experiments on the FOTON-M3 mission in 2007. They have also traveled to the International Space Station and were aboard the Israeli lunar lander Beresheet, which crashed on the Moon in 2019. Their presence extends to other harsh terrestrial locations, including deep-sea hydrothermal vents, the peaks of the Himalayas, frigid polar regions like Antarctica, and the cryptobiotic soil crusts of deserts.
Finding Tardigrades Yourself
Tardigrades are microscopic, typically ranging from 0.1 to 1.5 millimeters.
The most accessible places to find tardigrades are damp moss and lichen, which can be collected from trees, rocks, or even your own backyard. You can also find them in pond water, leaf litter, or damp soil. To collect a sample, gently scrape a small amount of moss or lichen into a container, such as a petri dish. Add non-tap water, like distilled or spring water, until the sample is submerged, and let it soak for at least a few hours, or ideally overnight, to allow any dormant tardigrades to rehydrate and become active. After soaking, gently squeeze or shake the moss over the container to release the tardigrades into the water, then allow any debris to settle to the bottom.
A stereo microscope with 20x to 50x magnification is suitable for initial spotting, while a compound microscope offering 40x to 400x magnification will provide a more detailed view of their features. Many can be seen even at 40x total magnification. Use a pipette or dropper to transfer a small amount of the water from your sample onto a microscope slide, then cover it with a coverslip. Begin your search under low magnification, slowly scanning the slide. Patience may be needed as they reanimate and begin moving.