Why Do Scorpions Glow Under UV Light? One Scientist Has Some Theories

Next time you go hunting for scorpions under cover of darkness, here’s a handy hack: Bring a black light. Most scorpion species are fluorescent, meaning they glow—in this case, a dazzling bluish green—when exposed to ultraviolet (UV) light.

Like certain other glowing animals, it’s not exactly clear why scorpions have this talent, but scientists have theories. And in the following YouTube video, Veritasium host Derek Muller explores some of them with Carl Kloock, a biology professor at California State University Bakersfield who’s devoted more than 10 years to solving the mystery.

Over the course of his research, Kloock has come up with several hypotheses to explain the phenomenon. One, as Nerdist reports, is simply that it’s a “relic trait”—some holdover from earlier on in scorpion evolution that no longer serves any purpose. It’s also been suggested that it functions as a natural sunscreen, which would’ve been especially critical back before the Earth’s ozone layer existed.

Another idea is that fluorescence helps scorpions entice prey. To test this, Kloock devised an experiment in which he blocked fluorescence in some scorpions and compared the number of flies they attracted at night to that of glowing scorpions. Under a full moon, when the scorpions’ fluorescence was at maximum capacity, the glowing ones attracted fewer flies, suggesting that the glow may actually hurt their ability to ensnare a snack.

Kloock believes the most likely explanation is that scorpions use their fluorescence to detect light. He conducted an experiment to test this, too, which entailed putting fluorescent and nonfluorescent scorpions in half-covered containers and then exposing them to UV light. The light didn’t affect the nonfluorescent specimens’ behavior, whereas the glowing ones spent more time in the covered half of the container. It’s possible that, once a scorpion realizes it’s a bright night, it may decide to seek shelter for fear of being seen too easily by some predator.

Watch the video below to hear more details and see the neon creatures in action.