Why fungi nightlights are glowing in the rain forest

On a dark enough night in the Brazilian rain forest, aside from the dancing lights of fireflies, your journey can be softly illuminated by the green glow of Neonothopanus gardneri. The fact that this mushroom glows at the base of babassu palms each night isn’t really in question. The question has been why they’ve evolved to go from beige in daylight to monster-movie green at night.

A first step towards understanding this was the realization that they’re not glowing all the time. Since a possible explanation had once been that the glowing was just a coincidental byproduct of the mushroom’s metabolism, the discovery of an internal clock that synced their glowing to nighttime hours provided evidence that this was a more sophisticated, beneficial system. If the mushrooms bothering to turn the lights out during the day, there must be some advantage to turning them on at night.

Who’s interested in glowing mushrooms?

A recent test demonstrated that the allure of the night may be the audience available at that time, such as small insects. Researchers put fake mushrooms in the forest, some with matching green lights, some without, and all with a sticky outer layer. The next day, they went to look for evidence of who or what may have come into contact with the mushrooms overnight, and if there was any difference between the lit and unlit mushrooms.

As predicted, the glowing faux-fungi had significantly more bugs stuck to their surface, indicating that the insects are drawn to the light. The hypothesis then goes that the mushrooms’ light attracts the insects, who visit and then spread spores across the forest. It’s sort of a night-club version of being a colorful flower that wants bees to visit and spread pollen. The one missing piece there is if the mushroom provides an equivalent to nectar to its visitors, or if the dazzling lights are enough to draw in spore-carriers.

Source: Why Some Mushrooms Glow In The Dark by Nell Greenfieldboyce, Weekend Edition Saturday