This prescient study reveals that bioluminescent mushrooms in the jungles of Brazil glow in the dark to attract insects leading to spore dispersal via tiny "mule trains" in the absence of wind currents that would normally disperse spores aerially. How and why organisms as diverse as aquatic diatoms and jellyfish to fireflies emit light has fascinated biologists young and old. The studies reported here extend our understanding to mushrooms, showing conclusively and elegantly that they produce light in a circadian fashion. Following entrainment with a 12 hour dark/light cycle, the investigators simply captured images of the mushrooms with a CCD camera every hour over a six day period, revealing circadian rhythmicity! The circadian oscillator was found to be temperature compensated, with a 22 hour rhythm at 21, 25, or 29°C. The biochemical basis for this clock is a circadian cycling of the enzymatic activities that produce the light, as shown biochemically in tissue extracts for luciferase, an NAD(P)H-dependent reductase, and the substrate luciferin.