Bioluminescent Animals: 15 Creatures That Make Their Own Light

How does bioluminescence work?

The basic recipe is simple. Luciferin (from the Latin for “light-bearer”) reacts with oxygen, and the luciferase enzyme speeds up the reaction. The product is left in an energized state and releases that energy as a photon of light. Some animals, such as the firefly, also need the cell’s energy molecule, ATP. Others store the ingredients together as a photoprotein that flashes when calcium is added.

The light comes with very little heat, so it is often called “cold light.” Luciferins vary little between groups; one called coelenterazine occurs in at least 11 animal phyla, and some animals get it from their food. Luciferases, by contrast, differ widely, which shows that bioluminescence has evolved independently many times, at least 40 and possibly more than 90.

Not every glowing animal makes its own chemicals. Some anglerfish and squid farm luminous bacteria in special light organs and use the bacteria’s light.

Bioluminescence vs fluorescence

A bioluminescent animal can glow in complete darkness. A fluorescent animal cannot: it absorbs light, usually ultraviolet or blue, and re-emits it at a longer wavelength. That is why scorpions glow under UV light but are invisible in a dark room. Some animals combine both: the crystal jelly makes blue light, and a fluorescent protein turns it green.

Why do animals glow?

Biologists recognize five main uses for living light:

• Finding a mate: fireflies and sea fireflies flash species-specific codes.
• Luring prey: anglerfish and New Zealand glowworms use light as bait.
• Camouflage: many fish and squid light up their bellies to match the faint light from above, hiding their silhouette from predators below. This is called counterillumination.
• Defense: some animals startle attackers with a flash, release a glowing smoke screen or light up a predator so that something bigger will notice it.
• Warning: a glow can tell predators that an animal tastes bad or is toxic.

1. Fireflies

Fireflies are not flies but beetles of the family Lampyridae, with more than 2,400 described species. Light organs on the abdomen flash in patterns that differ between species, so males and females can find their own kind. In North America, females of the genus Photuris copy the flash pattern of Photinus females to lure their males, then eat them.

The common eastern firefly of the eastern United States flashes a rising “J” stroke at dusk in early summer. For the full story of how and why they light up, read Why do fireflies glow?

2. European glow-worm

The common glow-worm (Lampyris noctiluca) is also a firefly beetle and is found from Britain and Portugal across Europe and Asia to China. The wingless females climb grass stems on summer nights and glow a steady green-yellow to attract flying males. The larvae, which also glow faintly, hunt snails and slugs.

3. New Zealand glowworm

The New Zealand glowworm (Arachnocampa luminosa) is the larva of a fungus gnat. It lives on cave ceilings and damp, shaded banks, where it hangs dozens of silk threads beaded with sticky droplets. Its blue-green glow attracts small flying insects, which get trapped in the threads. Thousands of larvae light up the ceilings of caves such as those at Waitomo on New Zealand’s North Island.

4. Sierra luminous millipedes

Millipedes of the genus Motyxia, found only in the mountains of California, glow green-blue at night. Like their relatives, they can release cyanide when attacked. In a 2011 field experiment, glowing clay models of the millipedes were attacked less often by night predators than dark ones, evidence that the light works as a warning.

5. Anglerfish

Female deep-sea anglerfish carry a fishing rod: a modified fin spine tipped with a lure called the esca. In many species the esca is packed with glowing bacteria, and the fish waves it in front of its huge mouth to attract prey in the dark. The humpback anglerfish, found in all the major oceans, is a classic example. Learn more in Why do anglerfish have a light?

6. Lanternfish

Lanternfish (family Myctophidae) are small fish covered in rows of light organs called photophores, arranged in a pattern unique to each species. They are among the most abundant vertebrates on Earth and may account for up to 65% of the weight of all deep-sea fish. Each night many species rise toward the surface to feed and sink back to the depths before dawn.

7. Stoplight loosejaw

The stoplight loosejaw (Malacosteus niger) is a deep-sea dragonfish that produces red light as well as blue. Most deep-sea animals cannot see red, so the fish can light up its prey without being noticed, like a private searchlight. To see its own red light, it uses a pigment related to chlorophyll in its eyes.

8. Kitefin shark

The kitefin shark (Dalatias licha) is the largest known luminous vertebrate. It usually grows to 1–1.4 m (3.3–4.6 ft), sometimes more, and lives in deep water in many oceans. Its belly gives off a faint blue glow, which probably helps hide it from below. Researchers working off New Zealand confirmed its glow in 2021.

9. Firefly squid

The firefly squid (Watasenia scintillans) is only about 7.5 cm (3 in) long, but it carries 800–1,000 tiny photophores on its underside and three large light organs on the tip of each of two arms. Every spring, huge numbers come to the surface to spawn in Toyama Bay, Japan, where their blue light draws crowds of visitors.

10. Hawaiian bobtail squid

The Hawaiian bobtail squid (Euprymna scolopes) is a thumb-sized squid that hosts glowing bacteria, Aliivibrio fischeri, in a light organ on its underside. At night, it adjusts the light to match the moonlight from above, so it casts no shadow for predators below. Each morning at dawn it expels up to 95% of the bacteria, and the rest regrow during the day.

11. Vampire squid

Despite its name, the vampire squid (Vampyroteuthis infernalis) is neither a true squid nor an octopus, and it eats drifting debris called marine snow, not blood. It lives in deep, low-oxygen water. When threatened, it can release a cloud of sticky, glowing mucus from its arm tips to confuse a predator while it slips away.

12. Crystal jelly

The crystal jelly (Aequorea victoria) of the North American Pacific coast shows a ring of green light around the edge of its bell. A photoprotein called aequorin makes blue light, and green fluorescent protein (GFP) turns it green. GFP became one of the most important tools in biology, used to tag cells and genes, and its discovery earned Osamu Shimomura, Martin Chalfie and Roger Tsien the 2008 Nobel Prize in Chemistry.

13. Atolla jellyfish

The deep-sea Atolla jellyfish responds to an attack with a spinning ring of blue flashes. Scientists think this “burglar alarm” calls in larger predators that may eat the attacker. The ocean scientist Edith Widder built an electronic lure that mimics the display, and it helped attract the giant squid that was filmed in its natural habitat for the first time in 2012.

14. Comb jellies

Comb jellies, or ctenophores, are not true jellyfish. The rainbow shimmer that runs along their bodies by day is not bioluminescence at all, but light scattered by rows of beating hair-like cilia. Many species, however, also make real light: the warty comb jelly (Mnemiopsis leidyi) and others give off blue-green flashes when disturbed in the dark.

15. Sea fireflies

Sea fireflies are ostracods, tiny crustaceans about 2–3 mm long. The Japanese species Vargula hilgendorfii squirts luciferin and luciferase into the water, making a cloud of blue light. In the Caribbean, male ostracods produce dotted trails of light as courtship signals. During World War II, the Japanese army sometimes used dried sea fireflies as a dim light for reading maps.

What makes the sea glow?

Glowing waves on beaches in California, Wales or the Maldives are usually caused by dinoflagellates, single-celled plankton such as Noctiluca scintillans (“sea sparkle”). They are not animals, but they use a luciferin-luciferase reaction too, flashing blue when waves or swimmers move the water. Puerto Rico’s bioluminescent bays, such as Mosquito Bay on Vieques, owe their glow to another dinoflagellate, Pyrodinium bahamense.

Deeper down, most of the light comes from animals. Explorers in submersibles describe sparks, flashes and glowing clouds every time they move. To meet more of the creatures living there, see our list of deep-sea animals.