Why Scorpions Glow in the Dark

Scorpions are incredibly fluorescent and glow bright neon green under ultraviolet light due to fluorescence, which means their bodies absorb UV light and reradiate it in the visible spectrum.

Scorpions can be easily spotted in the desert at night using an ultraviolet torch, making them surprisingly simple to locate.

• Jellyfish fluoresce under ultraviolet light • Amphibians glow under UV light • Owls display fluorescence properties • Platypuses glow under ultraviolet light

Carl Kloock, a professor of biology at Cal State Bakersfield, has been researching scorpion fluorescence for over a decade.

One hypothesis was that scorpions fluoresce to attract insects for feeding purposes.

Carl used preserved scorpions, coating half with UV blocking marine varnish so they didn't fluoresce, then placed them on flypaper outdoors to measure insect attraction under different moon phases.

• Under new moon: no difference in insects caught between fluorescent and non-fluorescent scorpions • Under full moon: fluorescent scorpions caught fewer insects than non-fluorescent ones • This counterintuitive finding contradicted the original hypothesis

Fluorescence is not used to lure insects; in fact, it appears detrimental to the scorpion's ability to catch flying insects.

Scorpions have eight eyes total: two median eyes and a cluster of three eyes on each side, arranged symmetrically on their body.

In a 1968 experiment, scorpions with painted-over eyes still detected light 93% of the time and moved to covered areas, proving they can sense light with their bodies, not just their eyes.

Scorpions possess an extraocular light sense in their tail, allowing them to detect light without forming images.

• Communicate with other scorpions of the same species for mating • Act as camouflage by absorbing UV light to blend with surfaces • Detect predators that see in ultraviolet light

Scorpions came out of the water during the Silurian period when there was significantly more UV radiation in sunlight due to the absence of an ozone layer.

• Relic trait: something developed when they first came on land that hasn't been lost • Byproduct: a chemical with another function that happens to fluoresce • Sunscreen: absorbs damaging ultraviolet photons and converts them to prevent body damage

Internal bodily fluids in scorpions fluoresce, suggesting fluorescence isn't necessarily functional but simply a chemical property.

Scorpions can metabolize iron and nickel, which they use to strengthen their pincers and claws.

Carl developed a technique to reduce scorpion fluorescence by exposing them to long periods of ultraviolet light, photobleaching the fluorescent chemical in their exoskeleton.

• Non-fluorescent scorpions exposed to UV light showed no behavioral change from darkness • Fluorescent scorpions significantly reduced activity levels when exposed to UV light • This demonstrated fluorescence functions as a light detection mechanism

Fluorescence acts as a whole-body photon detector, allowing scorpions to sense ultraviolet light through their entire body rather than just their eyes or tail.

The suspected function is to help scorpions determine whether they should come out at night, using UV light levels as a cue for predation risk and foraging necessity.

Scorpions can survive long periods without eating and are reluctant to forage during bright moonlit nights when predation risk is highest.

Scorpions use UV light levels as an environmental cue to gauge how bright it is and therefore how likely they are to be preyed upon.

During full moons, only scorpions that are very hungry and need food will venture out, while well-fed scorpions remain in their holes.

Scorpions balance two factors when deciding whether to forage: environmental brightness (predation risk) and their hunger level (food necessity) to determine the best course of action.