Light-making life is everywhere -- you just have to look in the dark. Here are some of the most remarkable glowing organisms on Earth, in the sea, on land and in the forest.
The ocean is where bioluminescence truly rules. Below about 200 meters, sunlight fades to almost nothing, and for many animals the only light they will ever see is light made by other living things.
Female deep-sea anglerfish carry a fishing-rod-like spine tipped with a glowing lure called an esca. The light is not made by the fish itself but by bacteria living inside the lure.
In the near-total darkness of the deep, a small glowing spot is irresistible to curious prey -- which swim right up to a mouth full of needle-like teeth.
Despite the name, the vampire squid is a gentle drifter that feeds on falling marine snow. Its arm tips can glow, and instead of squirting ink it can release a cloud of sticky, glowing mucus.
The glowing cloud may distract a predator while the squid swims off into the dark.
Lanternfish are small fish covered in rows of light organs called photophores. The pattern of lights differs from species to species, which scientists use to tell them apart.
They are among the most abundant fish on Earth. Many rise toward the surface at night to feed and sink back down at dawn -- part of the largest daily migration of animals on the planet.
This nearly transparent jellyfish glows green around the rim of its bell. A protein called aequorin makes blue light, and a second protein -- green fluorescent protein, or GFP -- turns that blue light into green.
GFP became a revolutionary tool for tagging and watching cells and genes. Its discovery and development earned the 2008 Nobel Prize in Chemistry.
When attacked, this deep red jellyfish produces a spinning ring of blue flashes. Scientists think this "burglar alarm" display may attract a bigger predator that will go after the attacker.
An electronic lure that imitates the Atolla display, called the e-jelly, helped researchers film a giant squid in its deep-sea home for the first time, in 2012.
This thumb-sized squid keeps glowing bacteria (Vibrio fischeri) in a special light organ on its underside. At night, it uses the light to match the moonlight from above, erasing its own shadow so predators below cannot see its silhouette.
Every morning the squid vents most of the bacteria into the sea, and the remaining ones regrow during the day.
Most deep-sea light is blue, and most deep-sea animals cannot see red. The stoplight loosejaw is a dragonfish that makes red light from organs under its eyes -- and it can see that red light itself.
That gives it a private searchlight for spotting prey that never sees it coming.
Several sharks glow. The cookiecutter shark has a glowing belly with a dark collar that may look like the silhouette of a small fish to hungry predators -- which then get a round bite taken out of them instead.
In 2021, researchers reported that the kitefin shark, which can grow to about 1.8 meters (about 6 feet) long, is the largest known glowing animal with a backbone.
These tiny crustaceans, about the size of a sesame seed, squirt out two chemicals that react in the water to make a bright blue glow.
In the Caribbean, male ostracods perform courtship displays, leaving trails of glowing dots in the water in patterns specific to their species.
These single-celled plankton are behind most glowing waves and bioluminescent bays. Each cell flashes when the water around it is disturbed, so a paddle, a fish or a breaking wave lights up in blue.
One leading idea is the "burglar alarm" again: a flash may startle small grazers or draw in bigger predators that eat them.
Glowing land animals are rarer than glowing sea life, but they include some of the best-loved sights in nature. No land animal with a backbone is known to make its own light.
Fireflies are not flies; they are beetles. Many species flash in a pattern unique to their species, and males and females use these codes to find each other in the dark.
Some predatory Photuris females mimic the flash replies of other species to lure in males -- and then eat them. Firefly larvae glow too, which is thought to warn predators that they taste bad.
These "glowworms" are the larvae of a fungus gnat. Each one hangs down sticky silk threads and glows blue-green from its tail.
Small flying insects are drawn to the light and get caught in the threads. A cave ceiling full of them looks like a starry night sky.
Not a worm but a beetle larva, the railroad worm has a row of green-yellow lights along its sides and a red light on its head -- like the windows and headlamp of a train at night.
It is one of very few land animals known to make red light.
These millipedes glow a soft green-blue at night. They also defend themselves with cyanide-based chemicals, and the glow appears to warn nocturnal predators to stay away.
Some click beetles have two bright lights on their thorax that glow steadily, like a pair of headlights, plus another light underneath that shows when they fly.
Glowing fungi shine a steady green, often all night. You usually need a very dark forest, a moonless night and a few minutes for your eyes to adjust before you notice them.
Foxfire is the eerie green glow of rotting wood infected with fungal threads. People have noticed it for thousands of years; the ancient Greek writer Aristotle described a light from decaying wood that did not feel hot.
A pale mushroom that glows a ghostly green at night. It is poisonous, and so is its glowing relative the jack-o-lantern mushroom (Omphalotus olearius) found in Europe and North America.
Many of the more than one hundred known glowing fungi are small bonnet mushrooms in the genus Mycena. Some glow from the cap, some from the stem, and some only from their threads hidden in wood.
Research on one Brazilian glowing mushroom found that its glow attracts insects, which may help spread its spores.
Many glowing sea creatures do not make light themselves. They farm it. Anglerfish, bobtail squid and some other fish host glowing bacteria in special organs, giving the bacteria food and shelter in exchange for light.
Glowing bacteria also taught scientists something big. Studies of Vibrio fischeri showed that the bacteria only switch on their light when enough of them are crowded together. They detect their own numbers by sensing chemical signals, a process now called quorum sensing, which turned out to be used by many kinds of bacteria, including some that cause disease.
On rare occasions, sailors have reported huge patches of ocean glowing a steady milky white through the night. These "milky seas" are thought to be caused by vast numbers of glowing bacteria, and satellite images later confirmed one in 1995 covering an area the size of a small country.
