For most people, the most familiar source of bioluminescence is the firefly. Along with charming nighttime displays, these insects have contributed an important tool to the scientific community: luciferases, which have become common genetic reporters and alternatives to fluorescent proteins. The North American firefly, Photinus pyralis, catalyzes a chemical reaction in its abdomen to produce yellow-green light (Figure 2). Despite the title of this post, this reaction is not fluorescence!...