The term ‘bioluminescence’ refers to the production of light by living organisms which is emitted from their body. This light is created by the organism either through a series of chemical reactions (typically a substance called luciferin reacts with oxygen as a chemical reaction to release energy in the form of light), or by a form of glowing ʙᴀᴄᴛᴇʀɪᴀ that the animal hosts.
Beetles whose flash punctuate summer skies; ᴋɪʟʟer fish that lure prey with an enticing light; algae that rat out their ᴀᴛᴛᴀᴄᴋers with a telltale glow. These ᴏᴍɪɴᴏᴜs organisms might seem like creatures from out of this world, but thanks to some clever chemistry, such beings are in fact abundant on our planet. Examples of creatures that generate their own light—a capability known as bioluminescence—are especially common in the ocean, where filmmaker James Cameron purportedly drew inspiration for the glimmering alien life in his new sci-fi flick Avatar.
Although bioluminescence is rare on land, with no recognized plant or vertebrate species producing such light, diverse critters from insect larvae to mushrooms to ᴏᴏᴢᴇ-secreting earthworms have shown that they can shine. Overall, scientists think bioluminescence has independently evolved at least 40 different times across the animal, fungal and ʙᴀᴄᴛᴇʀɪᴀl kingdoms, “which is a clear indication of the survival value of the trait,” says Edie Widder, co-founder, president and senior scientist at the Florida-based Ocean Research and Conservation Association (ORCA). There are a range of practical reasons animals have evolved this special power. Animals produce light and use bioluminescence to:
- Fend off ᴘʀᴇᴅᴀᴛᴏʀs
- Lure prey
- Camouflage themselves
- Attract mates
- Communicate with one another
In fact, making light has proven to be such a useful trait that it has evolved independently at least 40 times.. Even in dim or dark environments where the sun’s rays cannot penetrate, such as caves or much of the oceans, many animals still have eyes—oftentimes extra-large ones—in order to glean information from the few stray photons available. Some 80 to 90 percent of deepwater, oceanic life has developed the ability to produce light, taking advantage of the transparent, though predominantly dark, medium in which it lives.
“I do believe we have just scratched the surface of what is out there,” says Karen Osborn, a postdoctoral fellow at the Scripps Institution of Oceanography at the University of California, San Diego. Given how often bioluminescence appears in earthly life, it seems a little less far-fetched to suppose that extraterrestrial life, as imagined in Avatar, might gleam, as well.
With all of this background and context in mind, below we feature some of the world’s craziest and coolest bioluminescent organisms:
1. Click Beetle
The Pyrophorus is a type of click beetle found in the Americas, also known as fire beetles because of their bioluminescence. Their glow is similar to the firefly, though they do not flash, but rather maintain a constant glow from the two luminescent spots on their back. At night they use their light to attract other insect prey to eat. Their eggs and larvae are also luminous.
2. Angler Fish
The angler fish lives in the deep sea (the lightless bottom of the Atlantic and Arctic oceans), and has a huge head with crescent-shaped mouths complete with plenty of sharp, translucent teeth.
Their name comes from the fleshy piece of dorsal fin the projects over their mouth to attract prey. There are over 200 species of anglerfish, usually dark gray to dark brown in colour, and anywhere from 0.3 to 1 meter in length.
3. Sea Salp
Salps are marine animals that resemble jellyfish, but they are actually chordates or animals with a dorsal nerve chord. Shaped like a barrel, these tiny free-swimming animals drift in the ocean individually or form colonies that stretch several feet in length. Salps are filter feeders that feed primarily on phytoplankton, such as diatoms and dinoflagellates. They play an important role in marine ecosystems by controlling phytoplankton blooms. Some salp species are bioluminescent and use light to communicate between individuals when linked in vast chains. Individual salps also use bioluminescence to attract prey and potential mates.
4. Glow Worm
We need to be careful with glow worms as the word means different things in different continents. In Europe, glow-worms refer to the non-flying wingless species in the Lampyridae family, which emit a steady glow (unlike the short bursts of the fireflies). The Lampyridae family has over 2,000 species, with new species still being discovered.
In the Americas, glow worms refers to another luminescent beetle group (Phengodidae) and in Australia and New Zealand the name refers to the glowing larvae of fungus gnats, Arachnocampa.
Black dragonfish are ᴍᴏɴsᴛʀᴏᴜs-looking, scaleless fish with very sharp, fang-like teeth. They are typically found in deep sea aquatic habitats. These fish have specialized organs known as photophores that produce light. Tiny photophores are located along its body and larger photophores are found below its eyes and in a structure that hangs below its jaw known as barbel. Dragonfish use the glowing barbel to lure fish and other prey. In addition to the production of blue-green light, dragonfish are also capable of emitting red light. Red light helps the dragon fish locate prey in the dark.
Fireflies are those species of the Lampyridae family that are able to fly, where the male and female are similar in appearance and emit light as short flashes to attract mates. The females of some firefly species actually mimic the light patterns of other firefly species, luring males to the ground where they ᴋɪʟʟ and eat them… it’s a ᴅᴀɴɢᴇʀous world!
Jellyfish are invertebrates that consist of a jelly-like material. They are found in both marine and freshwater habitats. Jellyfish typically feed on dinoflagellates and other microscopic algae, fish eggs, and even other jellyfish.
Jellyfish have the ability to emit blue or green light. A number of different species use bioluminescence primarily for defense purposes. The light emission is typically activated by touch, which serves to startle ᴘʀᴇᴅᴀᴛᴏʀs. The light also makes ᴘʀᴇᴅᴀᴛᴏʀs more visible and may attract other organisms that prey on jellyfish ᴘʀᴇᴅᴀᴛᴏʀs. Comb jellies have been known to secrete luminescent ink that serves to distract ᴘʀᴇᴅᴀᴛᴏʀs providing time for the comb jelly to escape. Additionally, bioluminescence is used by jellyfish to ᴡᴀʀɴ other organisms that a particular area is occupied.
While common in other cephalopods such as squid, bioluminescence does not typically occur in octopuses. The bioluminescent octopus is a deep sea creature with light-producing organs called photophores on its tentacles. The light is emitted from organs that resemble suckers. The blue-green light serves to attract prey and potential mates. The light is also a defense mechanism used to startle ᴘʀᴇᴅᴀᴛᴏʀs providing time for the octopus to escape.
9. Sea Snail
One of the most electric-looking creatures on this list, the sea snail is one of the dozens of species that use bioluminescence. It’s thought that sea snails actually use their opaque shells to diffuse and spread bright bioluminescent light in all directions, seemingly enlarging themselves to ᴘʀᴇᴅᴀᴛᴏʀs. Another school of thought says that sea snails use their glow for communicating without needing to leave the safety of their shell. Whatever it is, it sure is beautiful!
There are a number of species of bioluminescent squid that make their home in the deep sea. These cephalopods contain light producing photophores over large portions of their bodies. This enables the squid to emit a blue or green light along the length of its body. Other species use symbiotic ʙᴀᴄᴛᴇʀɪᴀ to produce light.
Squid use bioluminescence to attract prey as they migrate to the surface of the waters undercover of night. Bioluminescence is also used as a type of defense mechanism known as counter-illumination. Squids emit light to camouflage themselves from ᴘʀᴇᴅᴀᴛᴏʀs that typically hunt by using light variations to detect prey. Due to bioluminescence, the squid don’t cast a shadow in the moonlight making it difficult for ᴘʀᴇᴅᴀᴛᴏʀs to detect them.