Walk into a damp wood on a dark night, switch off your light and wait. At first there is nothing. Then a soft green glow slowly appears along a fallen log, or a cluster of tiny mushroom caps emerges among the leaves like a handful of little lamps.
Light without heat
The glow is called bioluminescence. Some fungi produce it through a chemical reaction in their cells, part of the same broad family of reactions that makes fireflies shine. Unlike fireflies, though, fungi do not flash. Their light is steady and faint, and often comes as much from the fine threads running through decaying wood as from the mushrooms themselves.
People have noticed it for centuries. In English it has long been known as “foxfire”, a fitting name for a light you often glimpse only out of the corner of your eye.
Why some fungi glow is still being studied. One theory is that the light attracts insects that help spread spores; another is that it is simply a by-product of fungal chemistry. For now, the forest keeps some of its secrets.
How to see it
Rain helps: the glow is often easier to spot when wood and soil are wet. Choose a night with little or no moonlight, stay away from street lamps and give your eyes plenty of time to adjust, longer than you might expect. If you need light to move around, a dim red light will help preserve your night vision.
Look, but do not pick. Glowing fungi are part of the slow work of turning dead wood back into soil, and some fungi are poisonous. Stay on the path, go with someone who knows the area and leave everything as you found it.
Then switch off your torch and wait. The forest is brighter than it looks.
