Pull up a cushion of moss and you are holding a small, crowded world. The damp, sheltered spaces between the leaves are home to a community of tiny animals, and one of them is among the toughest creatures known.
The water bears
Tardigrades, the "water bears", are eight-legged animals under a millimetre long that live in the film of water around moss leaves. When the moss dries, they dry too, curling into a desiccated tun and shutting their metabolism almost entirely off. In that state they have survived being frozen, boiled, irradiated and even the vacuum of space, springing back when wetted. Moss is the easiest place to find them: soak a dry cushion, squeeze the water into a dish, and look under a cheap microscope.
The rest of the crowd
They share the cushion with springtails, which flick themselves into the air with a sprung tail; mites; rotifers, the "wheel animalcules" that whirl food into their mouths; nematode worms; and the protozoa and bacteria they all feed on. A handful of moss can hold thousands of individuals across dozens of species.
Why moss is such good habitat
Moss does for these animals what it does for itself: it holds water, buffers the swings of temperature and humidity, and provides endless sheltered surface in a small space. Lose the moss from a wall or a wood and you lose this whole layer of life, and the larger creatures that feed on it. It is a reminder that the quiet green is doing more than it appears.
Look for yourself
Finding this world takes almost nothing. Collect a dry cushion of moss, drop it into a jar of water and leave it to soak for an hour or two, then squeeze the water out into a shallow dish or onto a glass slide. Under a basic microscope, even a cheap one or a clip-on phone lens at decent magnification, the drop comes alive: tumbling rotifers, scuttling mites, the unmistakable plodding gait of a tardigrade. Children find it spellbinding, and it costs the price of a jam jar. A drop from different mosses, or from a wall versus a wood, turns up noticeably different casts of characters.
A measure of a healthy place
The richness of that hidden community is also a quiet indicator. A moss cushion teeming with varied life sits in clean, undisturbed surroundings; a thin, sparse one often reflects pollution or disturbance nearby. Researchers lean on this, sampling the animals in moss as one read on the health of a habitat. For the gardener the lesson is gentler: a mossy, undisturbed corner is not a sign of neglect but a small reservoir of biodiversity, and leaving it be supports far more than the moss itself.