Millipedes of the Motyxia genus can safely wander through their mountainous California habitat at night without fear of becoming a midnight snack, thanks to a photoprotein—akin to green fluorescent protein—in their exoskeletons that gives the critters a greenish-blue glow. The creatures arm themselves with a cyanide chemical defense, but there had been speculation as to whether or not the bioluminescence served to warn would-be predators, such as mice, of its noxiousness. Now, a team led by University of Arizona entomologist Paul Marek has demonstrated in field tests that the luminescence does indeed prevent predatory attacks on the creepy crawlies (Curr. Biol., DOI: 10.1016/j.cub.2011.08.012). The researchers took 164 Motyxia sequoiae and painted half of them in a way that hid their bioluminescence. They also created 300 clay millipede models, painting half of them with a chemiluminescent pigment and the other half with the camouflaging paint. Nonluminescent millipedes and millipede models were attacked twice as often as their glowing counterparts. “This is the first field experiment in any organism to demonstrate that bioluminescence functions as a warning signal,” the researchers note.