Why Some Creatures Glow In The Dark

Animals that “glow in the dark” create a sense of fascination and wonder in people. From the time we are children catching fireflies at night, to the time we are adults and can just appreciate the beauty, the sense of attraction never ceases. However, have you ever wondered why certain animals emit that entrancing glow?

Front yard, Bernardsville, NJ

Some glow because they are flirting, or we should say, searching for mates. For example, fireflies, or lightening bugs, emit specific blinking patterns to help find potential mates. The Firefly is able to regulate their flashes by turn on or off its lights, as it pleases. The flashing is also completely unique to its species.

Another reason why an animal may glow is a use of defense. The ostracod is a small crustacean that spits out fire. Well, not exactly fire, but a bioluminescent liquid, that looks like a little fire, and deters predators. The crustacean spits out luciferin and luciferase that glow when they are mixed together. The clusterwink snail is also an example of this. The clusterwink diffuses a vivd green light without ever leaving its shell. Therefore, it remains protected and scares away its predator.


However, other use their seductive light to lure in prey. Nobody can forget the little light that went from being Dory’s cute “Squishy” and then to her and Marlin’s worst nightmare, in Finding Nemo. The scary Anglerfish lured them in with its dangling light. The light is attached to its dorsal spine and reals in prey like a fishing rod.

E. Widder/HBOI Melanocetus johnsoni

Others use bioluminescence as a camouflage. This usage is also called counterillumination because it matches the overhead environmental light. This is found in several species of squid. The animals have photoreceptors to control the illumination which allows them to match the brightness around them.