Glow-in-the-dark mushroom
Mushrooms glow in the dark to attract insects. Michele P. Verderane/IP-USP-2008

A fungal mystery that first perplexed Aristotle over 2,000 years ago has finally been solved – why mushrooms glow in the dark. An international team of researchers were looking at Neonothopanus gardneri, one of the biggest and brightest of bioluminescent mushrooms discovered.

Publishing their findings in the Cell Press journal Current Biology, researchers found the light emitted from mushrooms attracts insects – such as beetles, flies and ants – which are effective spreaders of fungal spores.

Cassius Stevani, of Brazil's Instituto de Química-Universidade de São Paul, explained: "It appears that fungi make light so they are noticed by insects who can help the fungus colonize new habitats."

Lots of living things generate light. Of the glow-in-the-dark organisms, fungi are the rarest and least understood. Only 71 of the 100,000 described fungal species produce green light in a biochemical process requiring oxygen and energy.

Previously, researchers had thought it was just a metabolic byproduct – albeit an expensive one. They thought in most cases they produced the light around the clock. However, in the latest study, researchers found the bioluminescence is under control of the circadian clock, suggesting it serves some sort of purpose.

N. gardneri – or flor de coco (meaning coconut flower) – are found attached to palm trees in coconut forests in Brazil. Researchers found their glow is under the control of a temperature-compensated circadian clock. This control likely helps the mushrooms save energy, the researchers said.

To study what the glow might do for the mushrooms, the team made sticky fake fungi from resin and lit some from the inside with green LED lights. These were placed where real mushrooms are found.

The glowing fake mushrooms attracted lots of insects – far more than the unlit ones – suggesting the insects help to spread the fungi spores. Researchers now plan to study the genes responsible for bioluminescence and are looking at the interaction with the circadian clock that controls them.

Working out how mushrooms are dispersed is important, as fungi species play a key role in forest ecosystem: "Without them, cellulose would be stuck in its form, which would impact the whole carbon cycle on Earth. I dare to say that life on Earth depends on organisms like these," Stevani said.