This time of year, “Rudolph the Red-Nosed Reindeer” is a nearly inescapable earworm. Rudolph, the old song goes, is bullied for having a nose so bright it glows (like a lightbulb!). But one Christmas Eve, his much-mocked nose makes Rudolph a hero. Using it as a beacon, Rudolph guides Santa’s flying sleigh through the foggy night to deliver gifts around the world.
Rudolph’s superbright snout might seem as fantastical as his ability to fly. But a light-up body part needs no holiday magic. Many animals glow through bioluminescence, and a built-in red headlight would make a great adaptive trait for a sleigh-pulling reindeer. Though thanks to physics, Rudolph’s nose