More than 2,000 years ago Aristotle noticed that certain mushrooms glow in the dark and asked why. Although there was no compelling answer in his lifetime, a team of researchers have finally come up with a good answer.

According to research published on March 19 in the journal Cell Biology, the light from the fungi attracts insects including wasps, ants, beetles and flies which spread the spores of the fungi and allow them to move into new areas.

This is similar to the evolutionary strategies of plants which use fruit, nuts and sweet nectar to attract animals which then spread the seeds. It is also similar to a, not uncommon, strategy used by some deep see animals which use bioluminescence to attract prey.

The authors of the new study show that the mushroom bioluminescence is controlled by a circadian clock.

A circadian clock or circadian rhythm indicates a 24 hour cycle which governs biological functions and behavior, with periodic adjustments for seasonal variations and other environmental changes.

It was the discovery that the bioluminescence of the mushrooms was controlled by a circadian clock that told the researchers that it must serve some useful biological function.

“Regulation implies an adaptive function for bioluminescence,” explains Jay Dunlap of Dartmouth’s Geisel School of Medicine in a statement.

Although there are plenty of examples of living things that generate light, it is very rare in fungi. Of the 100,000 described fungal species, only 71 produce light.

Many researchers had suspected that the fungi produced light constantly as some sort of metabolic byproduct.

However, the glow requires energy and oxygen and would be expensive and biologically undesirable as an accidental byproduct.

The new study, which was led by Dunlap and Cassius Stevani of Brazil’s Instituto de Química-Universidade de São Paulo, shows that, at least in the case of Neonothopanus gardneri, it is a useful strategy. The Brazilian mushroom, also called “flor de coco” or flower of the coconut flower frequently grow on the leaves at the base of young palm trees.

The mushrooms glow is dictated by a temperature-compensated circadian clock, which suggests that the mushrooms only “turn on the light” when it will do the most good. This, in turn, indicates that it is unlikely to be a accidental byproduct.

To find out what purpose the glow might serve, the team make fake mushrooms out of acrylic resin. Green LED lights were placed inside the mushrooms to simulate the glowing effect.

The researchers found that when their forgeries were placed in a forest setting where real bioluminescent mushrooms exist, the fake mushrooms attracted much more insect attention than those that were not lit.

“It appears that fungi make light so they are noticed by insects who can help the fungus colonize new habitats,” said Stevani.

According to Dunlap the research team is now interested in identifying the specific genes responsible for bioluminescence and exploring their interaction with the cicadian clock.

The researchers believe that understanding these things will provide insight into how mushrooms are dispersed in the environment. According to Stevani that information could be critical because of the mushrooms vital role in the 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,” said Stevani.