In the tropical forests of southern Mexico, twilight brings a quiet surprise. As the last light fades, tiny sparks begin to drift through the air around certain trees — faint greenish glows that seem to breathe from the bark itself. The forest floor shimmers with floating dots of light, as if the trees were exhaling stars.
The glow comes from bioluminescent fungi that live on decaying wood and tree trunks. These fungi release microscopic spores — tiny reproductive cells — that sometimes carry a faint glow of their own. The light is created by a chemical reaction between a substance called luciferin and oxygen, triggered by an enzyme known as luciferase. The same chemistry makes fireflies light up at night.
Green light only
The glow always falls within the green spectrum — easiest for nocturnal insects to see.
Ancient chemistry
The luciferin–luciferase reaction is thought to be millions of years old.
Scientists believe the glow may serve several purposes. One theory is that it helps attract insects, which then carry the spores to new patches of wood, spreading the fungi through the forest. Another idea is that the light deters animals that feed on fungi, making them appear toxic.
The phenomenon is most visible during the humid season in the rainforests of Oaxaca and Chiapas, where fallen logs and roots stay damp and alive with microbial life. To anyone walking through these woods, the sight can feel magical — as if the forest itself were breathing light.
What looks like enchantment is really ecology in motion: trees hosting luminous partners that turn decay into a brief moment of beauty before life begins again.