These glow-in-the-dark mushrooms might look like something from a 1960s black-light poster, but the luminous fungus Neonothopanus gardneri grows at the base of palm trees in Brazilian forests. The shrooms put on their light show to attract insects that will spread their spores, according to a study published online today in Current Biology. To test if that was the reason for the glow, the scientists placed plastic mushroom decoys at the base of trees, some lit with green LEDs to mimic the bioluminescence of the real thing. Over 5 nights, they counted the insect visitors to each imitation mushroom and found that those without LED light had far fewer: They collected a total of 12 insects from the dark mushrooms, compared with 42 from the glowing ones. In lab work, the researchers also showed that the mushrooms follow a daily rhythm, lighting up only when it's dark—presumably, an energy-conserving measure and another indication that their glow serves a purpose.