Why Do Some Living Things Glow?

An underwater glow. A fleeting gleam across a field. These lights seem mysterious, but organisms generate them for practical purposes. Bioluminescence fends off predators, lures prey, and attracts mates. Making light is such a useful trait that it has evolved independently at least 40 times. It occurs most commonly in the ocean, where bioluminescence is often the only source of light. Under the right conditions, a bioluminescent flash can be seen a hundred yards away.
(Read more about “Luminous Life” in this month’s issue of National Geographic.)

Click each illustration to see it animate


  • Surprise

    The prey produces a bright flash that startles a predator, making it easy to escape.

  • Smoke Screen

    The prey emits a glowing fluid or a cloud of sparks to misdirect the predator from its real location.

  • Decoy

    The prey jettisons one of its body parts. The luminescent limb distracts the predator, allowing escape.

  • Camouflage

    A shining underbelly matching the light from the surface conceals prey from predators below.

  • Alarm

    The prey’s bioluminescence makes its predator visible—alerting the predator’s predators.

  • Warning

    Gleaming prey signals to a predator that its next meal could taste terrible—or even be toxic.


  • Shock

    A burst of bright light from a bioluminescent predator stuns prey and leaves it open to attack.

  • Lure

    Like a moth to a flame, prey is drawn to the glow produced by a predator lurking all too close.

  • Beacon

    Predators seek out the glimmer that tells them that bioluminescent creatures are gathering.

  • Searchlight

    A predator turns on its natural spotlight to locate prey in a dark ocean.


  • Come-On

    Flickers of light signal that a bioluminescent insect is ready to meet new mates.

  • Invitation

    Mushrooms may spread their spores by using luminescence to entice insects to land on them.

Jason Treat and Daniela Santamarina, NGM Staff. Art: Eleanor Lutz. Animations: J. L. Wang. Source: Steven Haddock, Monterey Bay Aquarium Research Institute