Hundreds of marine animals fluoresce, all thanks to naturally occurring molecules that re-emit absorbed light at a different wavelength. Among the brightest of these molecules are green fluorescent proteins (GFPs). Some species use the light from GFPs to create a better environment for the symbiotic algae that live inside. Others use fluorescence to alter the colors of the light they actively emit through bioluminescence (which can serve as a burglar alarm and draw attention to nearby predators). Now, a new study finds that GFPs may also help some animals attract prey. Researchers came up with this idea while studying the flower cap jelly, Olindias formosus . This striped jellyfish lives in the western Pacific and catches small prey with its stinging tentacles, each of which has a fluorescent green band near the tip. Using a partitioned tank, the researchers recorded the young rockfish’s interest, under a variety of lights, in both the jelly and an artificial, tentacle-less jellyfish, called a blob object, that did not fluoresce. The fish were significantly more attracted to the jellyfish’s tentacles under blue lighting conditions — such as those found in the jellyfish’s natural environment — under which the fluorescence was excited and visible above the background light, the team reported July 31 in Biology Open . In a separate experiment, the fish chased similar-looking visual stimuli from a green laser pointer spot, confirming this strong attraction. The researchers suggest that the animals may mistake these fluorescent signals for those of chlorophyll, a pigment that plants and algae use to convert light into chemical energy through photosynthesis. Herbivores may mistake the fluorescence for chlorophyll from the algae they eat; Similarly, carnivores may think they’ve found a herbivore with chlorophyll in their guts. Following these tests, the researchers also discovered evidence of similar fluorescent lures in other marine creatures, including some fish, siphonophores, and a mantis shrimp.