Water bears, or tardigrades, are found on every continent on Earth, in nearly every habitat imaginable. These microscopic animals live in moss, lichen, leaf litter, soil, freshwater lakes, and ocean sediments. With over 900 described species, they’ve been collected from Himalayan mountaintops, Antarctic ice fields, deep sea vents, mud volcanoes, and tropical rainforests. But you don’t need to travel to extremes to find one. They’re almost certainly living in your backyard right now.
Their Favorite Habitat: Moss and Lichen
Despite their reputation as extreme survivors, most tardigrades spend their lives in a surprisingly ordinary place: the thin, damp layer inside moss and lichen. These plants hold a micro-thin film of water in their fissures through surface tension, creating tiny aquatic worlds. Tardigrades are true aquatic animals. Even species that live on land need to be surrounded by a film of water to feed, move, and reproduce. Moss and lichen provide exactly that, along with a food supply of plant cells and smaller organisms.
This is why moss is far and away the best place to look for tardigrades. A clump of moss scraped off a rock, a tree trunk, or a garden wall and soaked in water will often release dozens of them. They feed by piercing plant cells and sucking out the contents, or by eating even smaller creatures like rotifers and nematodes that share their micro-habitat.
Terrestrial, Freshwater, and Marine Species
Tardigrade species split roughly into three lifestyle categories. Terrestrial species are the most commonly encountered and live in moss, lichen, leaf litter, and soil. They depend on moisture from rain, dew, or humidity to stay active, and when their environment dries out, they curl into a dehydrated ball called a “tun” and wait, sometimes for years, until water returns.
Freshwater species live in the sediment of lakes, ponds, and streams. Marine species inhabit ocean floors, from shallow coastal sand to deep sea sediments. All three groups are genuinely aquatic in the sense that they require direct contact with water to carry out basic life functions. The terrestrial species simply get their water from much thinner, more precarious sources.
From the Himalayas to the Deep Ocean
Tardigrades have been documented across an enormous geographic and altitudinal range. They live at high elevations in the Himalayas, in the soils and mosses of Antarctica (where researchers have collected specimens near Lake Fryxell), in tropical rainforests, and at deep sea hydrothermal vents. They’ve been found in mud volcanoes, on rocky shorelines, and in the sediment beneath glaciers.
A recent discovery highlights how much is still unknown about their distribution. A wildlife ecologist at the University of North Texas identified previously undocumented tardigrade species on Navarino Island, a remote landmass at the southern tip of South America. Fieldwork in the temperate rainforests of southern Chile, funded by a three-year National Science Foundation grant, turned up both known and entirely new species, suggesting that tardigrade biodiversity in under-explored regions is far richer than current catalogs reflect.
Why They Survive Almost Anywhere
The reason tardigrades show up in so many places is their ability to shut down almost entirely when conditions turn hostile. When their environment dries out, freezes, or becomes otherwise unlivable, they pull in their legs, expel nearly all the water from their bodies, and enter a dormant state called cryptobiosis. In this form, they’ve survived temperatures as low as -200°C and as high as 151°C, X-ray radiation at 1,000 times the dose that would kill a human, the vacuum of outer space, and pressures six times greater than those at the bottom of the Mariana Trench.
This dormancy has limits, though. Laboratory studies show that survival drops sharply at temperatures above 55°C for dried specimens, and tardigrades exposed to cosmic radiation for two years in a dehydrated state failed to revive. They are tough, not invincible. In their active state, surrounded by water and going about their lives, they are actually quite sensitive to high temperatures and other stressors. The “indestructible” reputation applies specifically to the dormant tun form.
How to Find Them Near You
You don’t need to visit Antarctica or a hydrothermal vent. Tardigrades are common in urban and suburban environments wherever moss or lichen grows. Good places to collect samples include moss on roof tiles, stone walls, sidewalk cracks, tree bark, and garden rocks. Roof gutters that accumulate organic debris are another reliable source.
To see them, scrape a small clump of moss into a shallow dish and soak it in distilled or spring water for several hours. As the moss rehydrates, any tardigrades present will emerge from dormancy and begin moving. Under a basic microscope at around 40x magnification, they’re visible as plump, slow-moving animals with eight stubby legs, typically between 0.1 and 1.5 millimeters long. Their lumbering gait is what earned them the name “water bear” in the first place.