Tardigrades, or water bears, are one of the best things an amateur microscopist can find. They’re real animals, with eight stubby legs, claws and a slow, lumbering walk, and they’re surprisingly common. Many cushions of moss on walls, roofs, tree bark and pavements contain them. You don’t need a powerful microscope to find them: they’re big enough to spot at 10x to 40x. What you need most is the right moss and a bit of patience.
What tardigrades are
- Size: most adults are roughly 0.2–0.5 mm long, and the full range is about 0.1–1.5 mm. The larger ones are just visible to the naked eye as tiny white specks.
- Look: a plump, segmented body with four pairs of short, unjointed legs. Each leg ends in claws or, in some species, sticky discs. Many are translucent white or cream, while others are brownish, reddish or greenish, partly from what they’ve eaten. Some have two small dark eyespots.
- Habitat: thin films of water on moss, lichen, leaf litter and soil, as well as freshwater and the sea.
- Survival trick: when their habitat dries out, many moss-dwelling tardigrades curl into a dry, barrel-shaped state called a tun. In this state (a form of cryptobiosis), their metabolism almost stops. When water returns, they can rehydrate and become active again, often within an hour or so.
That last point is the key to finding them. Dry moss is fine, and often better. The tardigrades are waiting inside it for rain.
What you need
- A small clump of moss or lichen, about the size of a walnut
- A paper envelope or paper bag for collecting
- A shallow clear dish: a petri dish, jar lid or small saucer
- Water: rainwater, bottled spring water, or tap water left to stand for a day
- A plastic pipette or dropper
- A stereo microscope (10x–40x) if you have one, or a compound microscope at its lowest power
- Microscope slides, coverslips and ideally a cavity (depression) slide
- Tweezers
Where to collect
Tardigrades can turn up in many mosses, but some places are consistently better:
| Good places | Why |
|---|---|
| Cushion mosses on walls, roofs, gutters and pavement cracks | These mosses dry out and rewet often, and that suits tardigrades, which survive drying better than many competitors and predators |
| Mosses on tree bark | Often rich in tardigrades and rotifers |
| Silvery-green Bryum argenteum in sunny spots and between paving stones | Frequently recommended as a reliable source |
| Lichens on trees, rocks and walls | Some lichens host tardigrades, though yields vary |
| Leaf litter and the top layer of soil | Worth a try if you have no moss |
Tips for collecting:
- Take only a small piece, and only where you have permission. Leave plenty behind, and avoid protected sites.
- Collect into paper, not plastic. Damp moss sealed in a plastic bag can go mouldy. Letting it dry in a paper envelope does no harm to the tardigrades.
- Label it with the date and place. Different sites often give different results.
- Dry moss keeps. You can store dry, labelled moss for weeks or longer and soak a bit whenever you want to look.
Step-by-step: from moss to microscope
- Clean off loose soil. Shake off grit and pull away the soil at the base. Mud makes searching much harder.
- Soak the moss. Put it in your dish and add enough water to cover it. Leave it for a few hours, or overnight if the moss was dry. This gives tardigrades in the tun state time to rehydrate and start moving.
- Squeeze it out. Hold the moss over the dish with tweezers or clean fingers and squeeze it firmly, like a sponge, so the water drains into the dish. Some people also swish it about or tap it against the dish. Remove the moss and keep it in case you want to soak it again.
- Let it settle. Wait a minute or two. Tardigrades tend to sink and crawl about on the bottom, among the sediment.
- Search the dish. If you have a stereo microscope, put the whole dish on the stage and scan it systematically at 10x–20x, row by row. You’re looking for small, pale, plump shapes moving slowly with a clambering, leg-over-leg action. This is the easiest and most productive method.
- No stereo microscope? Use a pipette to take a drop of water and sediment from the bottom of the dish. Put it on a slide (a cavity slide is best), add a coverslip and scan the whole drop at the lowest power of a compound microscope, usually 40x. Check several drops.
- Move a tardigrade for a closer look. Once you spot one in the dish, suck it gently into a pipette with a little water and transfer it to a cavity slide or a fresh drop on a slide. Then you can view it at 100x and above.
How to recognise a tardigrade
A moss sample is a busy community. These are the animals most often confused with tardigrades:
| Organism | How it looks and moves | How to tell it apart |
|---|---|---|
| Tardigrade | Plump, segmented body; eight short legs with claws; slow, lumbering walk | Legs are stubby and unjointed; it clambers rather than swims |
| Rotifer | Often similar size; stretches and contracts like a telescope; may have a spinning “wheel” of cilia at the head; some move like inchworms | No legs; the rotating crown of cilia at the front is a giveaway when extended |
| Nematode (roundworm) | Long, smooth, thin and tapered at both ends; whips and thrashes in an S-shape | No legs, no segments; fast, wriggling movement |
| Mite | Eight legs, but long and jointed; moves quickly | Mites are arachnids, with jointed legs and a harder, often shiny body; tardigrade legs are soft stumps |
| Springtail and insect larvae | Six legs (springtails may jump); often larger | Count the legs: six, not eight |
| Protozoa | Single cells, often smaller; glide, spin or creep | No legs or segments |
You might also find:
- Tuns: if the moss didn’t soak long enough, you may see small, wrinkled, barrel-shaped bodies that don’t move. Leave them in water and check again later.
- Shed skins with eggs: some tardigrades lay their eggs inside the old cuticle when they moult. A transparent, empty-looking tardigrade outline containing a few round eggs is worth a closer look.
- Free eggs: some species lay eggs with elaborate spiky or ornamented shells.
Getting a good look
- Use a cavity slide so the coverslip doesn’t squash the animal. On a flat slide, support the coverslip on small blobs of petroleum jelly at the corners. Our guide to making a wet mount without air bubbles covers both techniques.
- Magnification: 40x–100x shows the whole animal walking. At 400x you can see the claws, the mouthparts (a tube with fine piercing stylets) and gut contents. Higher power needs the animal to be fairly still.
- Lighting: brightfield works. Darkfield lighting, from a darkfield condenser or a simple patch stop under the condenser, makes pale tardigrades glow against a black background and is lovely for photos.
- Slow them down: tardigrades are slow anyway, but they wander out of view. A few fibres of cotton wool in the drop give them something to cling to. Letting a little water evaporate also restricts their movement.
- Mind the heat: a bright lamp warms a small drop quickly. Turn the light down between looks.
- Photograph them: hold your phone to the eyepiece, or use an adapter; see whether you can turn your phone into a microscope. Video often works better than stills.
You don’t need any stain to see live tardigrades. Stains are unnecessary and would harm them.
If you can’t find any
Many people need a few samples before their first find. If you’re having no luck:
- Try a different moss. Some clumps contain none, and others contain many. Cushion mosses from exposed walls and roofs are often good.
- Soak longer. Tuns can take time to revive. Leave the moss overnight and search again.
- Squeeze harder and search the sediment, not the clear water.
- Search systematically. Scan the whole dish in rows rather than glancing around.
- Search at the right magnification. Too high and you’ll only see a tiny area. Start at 10x–40x.
- Look for movement. A moving tardigrade is much easier to spot than a still one.
- Rinse the moss and search the second batch of water. Sometimes more come out the second time.
Keeping tardigrades for a while
You can keep active tardigrades for a few days in a shallow dish of spring water or rainwater, with a little of the soaked moss, covered loosely to reduce evaporation and kept out of direct sun. Many moss tardigrades feed on plant cells, algae or other tiny animals, so the moss and its residents are their food. For longer-term observation, the simplest approach is to let the moss dry out again and soak it when you want to look. If you want to keep a specimen permanently on a slide, specialist media are used; see how to make permanent microscope slides.
When you’ve finished, return the moss outdoors.
Tardigrade facts, and a myth to ignore
- They’re tough in the tun state. In laboratory experiments, dried tardigrades of some species have survived extreme cold, high doses of radiation and very high pressures. In a 2007 experiment, some dried tardigrades survived exposure to open space in low Earth orbit and recovered back on Earth. Active, hydrated tardigrades are much more fragile.
- They aren’t from space. You may read online that tardigrades “came from space”. There’s no scientific support for this. They’re Earth animals, related to arthropods and velvet worms, and have a long evolutionary history here.
- There are many species. More than a thousand have been described, and identifying them usually needs high magnification and specialist keys.
If you enjoyed the hunt, there’s plenty more to find in the same moss water: rotifers, nematodes, ciliates and algae. Our guide to viewing microorganisms under a microscope is a good next step. For a family-friendly version of this project, see what kids can look at under a microscope.