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Nature's DayGlo: Creatures of the Ultraviolet Kind

The color spectrum is in the eye of the beholder.

Right under our noses there's a world of color visible to some eyes, but not to human's — the ultraviolet (UV) spectrum. UV wavelengths are too short for the human eye to see, but we're able to catch a glimpse of the otherwise invisible coloring under blacklight. Scientist are just discovering how widespread UV fluorescence is in the animal kingdom, and in many cases, researchers are left guessing as to its purpose. Check out some of the creatures that exhibit an incredible UV glow.

SCORPIONS ebettini SCORPIONS These arachnids are the most studied emitters of ultraviolet light. Some theories as to why they glow are to confuse prey, identify one another, or perhaps as protection from the sun. SCORPIONFISH Danita Delimont SCORPIONFISH These fish are named for their venom (not after land scorpion's similar spectral abilities), and many types of scorpionfish are designed for camouflage during the day. But when the lights go out, they're ready to rave in the equally florescent coral garden, perhaps providing a similar kind of camouflage at night. LEOPARD GECKO Albert Lleal/ Minden Pictures LEOPARD GECKO The leopard gecko is a nocturnal creature. One theory for UV glow in certain species is night aposematism, or the repulsion of a predator by color warning, similar to the way a brightly colored snake might indicate danger. HARVESTMAN (AKA DADDY LONGLEGS) Paul Bertner/ Minden Pictures HARVESTMAN (AKA DADDY LONGLEGS) With their glowing knees and beaming posterior, harvestmen are thought to possibly be using the spectral skill for mate selection. With poor vision, the bright light might help them find a partner at night. KATYDID Paul Bertner/ Minden Pictures KATYDID To capture the ultraviolet radiance of an animal like this on film, shots are taken in the dark, otherwise light will overwhelm the florescence. Photographers use an ultraviolet flash to capture images. HORNED LEAF Paul Bertner/ Minden Pictures HORNED LEAF They don't just change colors, many also glow. Their bones visibly fluoresce through their thin skin. Their skulls, in particular, glow so brightly, some hypothesize it's used for distinguishing between males and females at night. But scientists admit this is just a theory. MORAY EELS Ethan Daniels MORAY EELS These eels were discovered to be UV positive when one happened to photobomb a diver documenting ultraviolet corals on a night dive. MALAYSIAN STICK BUG Paul Bertner/ Minden Pictures MALAYSIAN STICK BUG This insect glows both blue and green. Though bright blue is the most common form of florescence, greens, pinks, purples, yellows, and reds can also be seen in animals. AEOLID NUDIBRANCH Borut Furlan AEOLID NUDIBRANCH Nudibranchs, also known as sea slugs, glow green and are also very brightly colored in daylight. SOLIFUGID SPIDER Albert Lleal/ Minden Pictures SOLIFUGID SPIDER Of the 41 genera of spiders, 19 glow under UV light, like this solifugid. LONG-ARMED HERMIT CRAB Borut Furlan LONG-ARMED HERMIT CRAB The hermit crab occupies a glowing shell, which it would have found, and perhaps chose because of its florescence, but its own body also glows green. ANGEL FISH AFP/AFP/Getty Images ANGEL FISH Almost the the entire body of this fish glows bright green. Fluorescence is unrelated to bioluminescence, which occurs in the human-visible spectrum, and is caused by a chemical reaction. Fluorescence can't be turned on or off, and it doesn't drain energy from the creature. MILLIPEDE KAdams66 MILLIPEDE Millipedes like this one glow very brightly under blacklight, as do some similar creatures like caterpillars. LICHED PREYING MANTIS Paul Bertner/ Minden Pictures LICHED PREYING MANTIS This liched preying mantis is a beautiful ultraviolet blue. Almost no mammals can see in ultraviolet, convenient for bugs that might be prey. Only one mammal can see in ultraviolet — the reindeer. Their ability to see in ultraviolet is thought to be related to their need to see in snow conditions. SEA ANEMONE Albert Lleal/ Minden Pictures SEA ANEMONE Sea anemone are living creatures (not plant life). Anemone glow brightly under UV, perhaps to lure in food. Anyone can use a blacklight at night to find animals, plants, fungi and minerals that fluoresce, but make sure to use safety measures and wear goggles!