Who doesn’t find things that glow in the dark fascinating?Imagine replacing the ’things’ with actual living beings. Interestingly, there are many types of animals that can actually glow in the dark, which is a little more fascinating than just ’things’ that light up!Did you know that there are many organisms on this planet that can produce light in their own bodies? We call these creatures bioluminescent. We find most of these creatures in the ocean (fish and invertebrates), whereas some fungi and fireflies are examples of bioluminescent organisms that can be found on land. Interestingly, did you know that there are almost no creatures that can glow found in freshwater habitats?Among the 8.7 million species that we know of, there are a huge number of animals that can emit light. Here, we’ll take a look at the phenomenon of bioluminescence that can be found in terrestrial and aquatic animals. Read on if you want to educate yourself some more about the different kinds of animals that can glow.How do animals light up?Some animals light up through a type of chemiluminescence called bioluminescence.The process usually takes place inside the animal’s cells. And these cells are usually located in a special light-producing organ known as a photophore. In some cases, these cells are distributed throughout the entire body of the animal or organism. The reaction occurs with the help of two molecules: luciferin and luciferase. Light is produced when the two molecules react with oxygen. This light is often called ‘cold light’ since it doesn’t contain a lot of heat, unlike, for example, rays of light coming from the sun or the heat generated by a fire. This light can be red, yellow, green, blue, or violet in color. But in the case of most aquatic creatures, it’s usually a green or blue light. And through water, blue light penetrates the deepest, which is why the sea or ocean appears blue to most people.An animal lights up when the light-producing pigment in their photophores, luciferin, reacts with oxygen, with the help of luciferase that works as a catalyzer. Sometimes there is a release of carbon dioxide as a waste product. And sometimes, the reaction requires other cofactors. For example, in the case of fireflies, the reaction needs the help of magnesium and ATP and produces carbon dioxide, AMP, and pyrophosphate. Jellyfish, on the other hand, use a photoprotein called aequorin instead of luciferase. With the help of calcium ions, the reaction produces a short flash of lightning. After the reaction, the oxidized luciferin (oxyluciferin) generates new luciferin for the next cycle of reaction to take place.Animals can usually control their glow by controlling the movement of oxygen in the photophores. But all the animals that are bioluminescent do not necessarily synthesize their own luciferin and luciferase. Some gain these by eating organisms that already have the molecules within themselves, whereas some host bacteria in their bodies for bioluminescence. These animals provide shelter and food to bacteria that are bioluminescent and get the bacteria to glow whenever they need it to.What animals glow in dark?Some well-known animals that can emit light are fireflies, angler fish, jellyfish, comb jellies, krill, firefly squid, giant squid, cookie-cutter shark, flashlight fish, sea fireflies, lanternfish, clusterwink snails, glowing sucker octopus, Tomopteris, and railroad worms.Other than these, certain Arthropods like specific types of click beetles (Pyrophorini, Balgus, and Campyloxenus), and glowworms are capable of emitting light. Some Mycetophilid flies, some centipedes, and certain millipedes can also glow in the dark too. A lot of marine animals and sea creatures are known to emit light. Many fungi, bacteria, and other microorganisms belong to this kind (bioluminescent) as well.Some of the fish that are bioluminescent are gulper eel, marine hatchet fish, midshipman fish, pineconefish, viperfish, black dragonfish, and many more. Many among the invertebrates have the ability to emit light. Most sea pens glow when stimulated. Over 60 species of brittle stars can emit a glow of light. Small Crustaceans like ostracods and copepods can radiate. Two types of arrow worms, a huge number of annelids, some clams, sea slugs, and sea snails, are also all capable of producing light. Some squids (colossal squid, firefly squid, whiplash squid), octopuses (such as Bolitaenidae), and vampire squids (such as bobtail squid) are also known to be bioluminescent too.What does bioluminescence mean?Bioluminescence is the biochemical process through which animals produce light and emit it.Bioluminescence usually requires luciferin (a molecule) and luciferase (an enzyme) in order to take place. Luciferase catalyzes the oxidation of the light-emitting molecule luciferin in order to produce light. But bioluminescence is not the same as biofluorescence. Because biofluorescence is not a chemical reaction but a process through which organisms absorb light energy and re-emit it. Some bioluminescent animals produce luciferin on their own, whereas, some absorb it from the bacteria they house in their light-emitting organs and have a symbiotic relationship with. The color of bioluminescence depends on the structure of luciferin and luciferase. The emission can be anything from red-yellow to blue-green light. This process has evolved at least 40 times, and it was already there during the Cretaceous period. At least 1500 species of fish are believed to be bioluminescent. Anything, from bacteria to sharks, can emit light. Bioluminescent creatures are organized into three categories: terrestrial, marine, and microorganisms.Why do animals light up?Different creatures use bioluminescence for a number of different purposes. The bioluminescent animals light up to camouflage themselves for protection, to attract mates, defend themselves against threats, warn predators, communicate with other animals, mimic other species in order to attract prey, and illuminate.Counterillumination, a method of camouflaging by producing light, is used by many deep-sea animals. They use this to match themselves with their backgrounds in brightness and wavelength. The specialized organs that produce light, typically located on the bottom of the marine animals, match the dim light that is coming from the surface. This combination can help to confuse predators below the animals, making it difficult to locate them.Some animals, like lightning bugs or fireflies, produce light in order to attract mates. Female fireflies emit light from their abdomen in order to attract males, whereas males use bioluminescent signals to which sedentary females typically respond to.Many animals often use bioluminescence for self-defense and to warn predators against approaching them. For example, some squids use a bioluminescent liquid instead of the traditional black ink to startle their predators. Whereas some jellyfish emit bright flashes of light to warn their predators away.New studies show that it is probable that, like some bacteria, some deep-sea bioluminescent animals use flashing patterns to communicate within their own species and attract partners.Deep-sea fish like the anglerfish and dragonfish are known to use mimicry to attract prey. The esca (appendage) on their heads have bioluminescent bacteria in them. These bacteria can produce strong beams of light that can be controlled by the fish. Using their esca, they mimic and lure smaller fish within their reach. Female Photuris fireflies mimic the pattern of flashing of another lightning bug called the Photinus firefly to lure its males as prey.Bioluminescence can not only be used to lure prey but also to locate them. Only some of the deep sea barbelled dragonfish are known to have the ability to produce red light, whereas other sea animals produce a green or blue light only. The red light allows the fish to locate red or reddish preys that cannot be seen in the depth and darkness of the ocean.Other Interesting Facts About Animals That Light UpThe color of the bioluminescent light varies based on the organism and its habitat. A huge number of aquatic animals have a blue or green glow, since these are the only colors visible to most of them. And most sea creatures cannot see red, violet, and yellow colors.Many land organisms, for example, fireflies and the only bioluminescent land snail called Quantula Striata, have a yellow glow. Whereas the head of the railroad worm glows red, and its body glows green.Some animals can emit light continuously, while some can turn their lights on and off. And some animals can also produce brief and quick flashes of lightning.Some insect larvae light up in order to warn predators and let the predators know that they are toxic.Sperm whales sometimes live with communities of bioluminescent planktons. When a fish predator approaches the planktons, they glow. And the sperm whale, alerted by the glowing, eats the fish. In this case, the planktons are neither symbiotes nor a diet.
Who doesn’t find things that glow in the dark fascinating?
