Bioluminescence – Animals that Glow in the Dark
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Isn’t nature amazing!? There are so many weird and wonderful things, but one of nature’s most impressive spectacles is bioluminescence. These glow in the dark animals are typically found in marine settings, although there are a few examples of this amazing phenomena on land.
There are lots of reasons that creatures may have the ability to illuminate, from mating to feeding and for communication. But one thing is for sure, it’s always an amazing sight!
What is Bioluminescence?
Bioluminescence is a word that refers to an animal’s ability to glow or light up. The process usually happens because of a chemical reaction or because of tiny glow-in-the-dark bacteria that live inside the creature.
When a chemical reaction occurs, this is typically because of sun rays that have been absorbed by the animal. This light is then transformed by the creature and emitted as light of a different color. But we will look at how animals glow in the dark in more detail later on.
What’s amazing is that, while most types of light also emit heat, bioluminescence doesn’t create any warmth. For this reason, it is often referred to as cold light.
Why Do Bioluminescent Animals Glow?
Watching an illuminated animal is certainly something worth getting excited about, but the question remains; why do bioluminescent animals glow?
The truth is that there are several reasons for this adaptation in certain creatures, but they’re all largely to do with the survival of the animal.
Attract prey – if you are a predator then you need to be able to see your prey. Many bioluminescent animals live in the depths of the ocean where there isn’t a lot of natural light, so having the ability to light up makes hunting easier. What’s more, some creatures will use the light to stun prey which makes it easier to catch.
Attract a mate – when it comes to mating, bioluminescence is a great way to attract a member of the opposite sex. This bioluminescence can help animals tell the difference between male and female when they are searching for a mate.
Communication purposes – some animals will use their bioluminescence in order to warn others that there is a predator nearby. This is known as a bioluminescent burglar alarm. In the darkest environments, light is often the only way to communicate with others of the same species.
Camouflage – while you might think that light would attract attention, it can actually be pretty useful for camouflage when the animal is in the reflection of the sun. This combined with their own bioluminescence can make them extremely difficult for predators to spot.
Scare predators away – while bioluminescence can help in catching prey, it also works the other way around and may help to deter predators. The light acts as a warning to potential predators, letting them know that this animal may be toxic.
How Do Animals Glow in the Dark?
Nature is pretty awesome when you think about it, even in the seemingly mundane ways, it’ll blow your mind. Knowing that animals can produce their own light sources is even more astounding. But just how do they actually manage this? Well, there’s a science behind it.
As we have already touched upon, bioluminescence is a type of cold light. So it’s different to the light emitted from the sun or even from something like a lightbulb. In order for this cold light to be able to occur, a chemical process is required.
Bioluminescent creatures have or produce as needed, a compound known as luciferin. When this chemical combines with oxygen, it creates light. There are even animals that absorb bacteria to create the chemical required for bioluminescence.
What is truly fascinating is that scientists are now looking at ways to use bioluminescence to benefit humans. Researchers in Denmark are looking at ways of isolating the gene used by bioluminescent animals and using it in trees. But why would they want to do that? To replace street lights, of course!
Imagine a more eco-friendly way of illuminating the streets at night than glowing trees lining every walkway. However, there could be something of a wait as the Danish company, Allumen, that is looking to achieve this feat isn’t the first to try.
Back in 2013, a similar project was attempted but was largely unsuccessful. There have been some attempts by MIT to cause a watercress plant to glow with some success. While the light only lasted a few hours and was relatively dim in the scheme of things, it could be an insight into future scientific work that could achieve the ultimate goal of greener nighttime street lighting.
Bioluminescent Animals on Land
The majority of bioluminescent animals can be found in marine environments but that isn’t to say that this miracle of nature can’t be found on land as well. Let’s take a look at some of the most wonderful land-dwelling bioluminescent creatures.
Fireflies (family Lampyridae)
Fireflies, also called lightning bugs, are perhaps one of the most well-known bioluminescent animals on the planet. These fascinating creatures can be found in almost every part of the USA as well as across South America, Asia, and some parts of Europe. Typically, they prefer open fields and areas around water, which is why they’re often found near riverbanks.
Fireflies emit a flashing light that serves to attract a mate. However, some female fireflies will produce light patterns that mimic those of other lightning bug species. When the males show up, she will eat them!
In order to create their bioluminescence, fireflies use a chemical process that mixes luciferin, oxygen, and a protein known as luciferase. When all of these things combine, the firefly will glow.
Railroad Worm (Phrixothrix hirtus)
One of the most interesting things about the railroad worm is that it is able to emit light in several different colors where other bioluminescent animals tend to emit yellow-green light. This beetle larvae uses a row of organs along its body to emit spots of light while its head gives off a red glow.
The lights on the body are used to attract a mate as the larva grows older, whereas the head light is used to aid in navigation.
Railroad worms earned their name from the similarity of their lights to the windows of a passing train. They are found from the northern parts of the US right the way down to Chile.
Glow Worms (family Lampyridae)
Glow worms are just the larvae of the firefly so it doesn’t come as much of a surprise that they can glow in the dark. However, unlike their parents, they aren’t yet able to emit that flashing glow. Instead, they have a single green light that comes from the head.
The purpose of their glow is twofold. Primarily it is used to attract prey but the glow worm also uses its light to warn off predators as they are toxic. Their light is produced using the same chemical reaction between luciferin, luciferase, and oxygen as their parents.
Glow worms are found across the United States and anywhere else that fireflies can be found. However, we should remember that outside of the USA, the term glow worm can be used to describe other creatures such as the larvae of the fungus gnat which is common in Australia.
Motyxia Millipede (Motyxia spp.)
The motyxia millipede is sometimes called the Sierra luminous millipede and is found in mountain ranges throughout California. While they may look amazing with their bioluminescent glow, these millipedes are actually very dangerous to predators as they produce cyanide! Their glow serves as a prior warning to potential predators to stay away!
They create their light via their exoskeleton, but while there are more than 12,000 species of millipedes, only around 9 to 11 are bioluminescent.
Bioluminescent Animals in the Ocean
While there are a number of bioluminescent animals on land, most of them are contained to the ocean. In fact, according to National Geographic, as many as 76% of all bioluminescent creatures are ocean-dwelling.
When we look at bioluminescent animals in the ocean, we notice that almost all of them emit some kind of blue light. The reason for this is that these light waves travel a lot further in the water and so have the most prominent effect. Imagine living in the dark depths of the sea and it’s easy to see why they’d need the most amount of light possible.
From jellyfish to sharks and everything in between, there are a surprising number of glowing creatures at the bottom of the sea. Let’s get better acquainted with some of them.
Cookiecutter Shark (Isistius brasiliensis)
Where clever hunting is concerned, the cookie-cutter shark certainly uses innovative natural resources. This shark, also known as the cigar shark, has a small bioluminescent patch on its belly that lights up due to special organs in the skin. When fish below see this, they assume it to be a smaller animal and will come to take a bite, only to be attacked by the cookie-cutter shark!
A member of the dogfish family, the cookie-cutter has a unique way of attacking its prey. Once the prey is attracted by the green light, the shark uses its sharp bottom teeth to attach and cut out the piece of flesh it wishes to eat; it’s easy to see where it gets its name.
The shark prefers tropical and temperate waters and has been found right from the western part of the Atlantic all the way to the Indo-Pacific.
Crystal Jelly (Aequorea victoria)
The crystal jelly is unlike other types of jellyfish as it is not considered to be a threat to humans. It is, however, an incredibly interesting creature that is able to emit a greenish-colored light owing to the presence of what is known as a green fluorescent protein, or GFP, for short.
The particular protein used by the jellyfish is called aequorin which is also used in science labs as a fluorescent marker. There was even one researcher that was able to use this GFP in order to make a rabbit glow! Although there is a considerable amount of controversy surrounding this research.
The crystal jelly will have a greenish light when under the rays of the sun, but if it is held under a UV light then its glow turns to a very clear green. It is believed that they emit this light when they are startled and as a defense mechanism against potential threats.
These animals are usually found along the Pacific coastlines of North America, running from Vancouver to California.
Yellow-Coated Clusterwink (Hinea brasiliana)
The yellow coated clusterwink is a type of sea snail that has some pretty amazing ways of emitting light. For starters, the snail is able to leave a trail of glowing mucus behind it and it does this in order to attract a mate. Moreover, the snail can create flashes of light from its body which are then diffused by its long conical shell. It is thought that it does this when it is startled as scientists found that the snail will flash when it is tapped.
Yellow coated clusterwinks can be found along the eastern coast of Australia and all the way across to New Zealand. They frequent rocky shorelines and it is thought that they use a similar chemical reaction to other bioluminescent animals to create their greenish glow.
Firefly Squid (Watasenia scintillans)
The firefly squid, which is also sometimes called the sparkling enope squid, has 1000s of tiny lights all along the length of its body. The main reason for its bioluminescence is thought to be as a way of attracting prey. However, there is also some suggestion that these creatures also use their light to aid in communication.
Found only in Japanese waters, the firefly squid tends to hang around the shoreline during mating season. In fact, the females make their last journey back to shore to lay their eggs before dying. For the rest of their lives, firefly squids remain at much deeper depths up to 400 meters.
These animals are able to create light thanks to organs within the skin known as photophores. They can glow between green, blue, and yellow.
Anglerfishes (order Lophiiformes)
Perhaps one of the most easily recognizable bioluminescent fish is the anglerfish. It’s featured in a whole array of horror stories of the deep and made a very notable appearance in the movie, Finding Nemo.
But despite their somewhat unusual appearance, anglerfish are extremely amazing creatures. They inhabit the very depths of marine waters, typically around 200 meters, although they have been found much deeper than this, up to 2000 meters!
Female anglerfish create light by allowing bioluminescent bacteria to inhabit their lure, which is known as the esca. This fleshy bulb dangles from the fish’s head and is used to attract prey. Once they come close enough, the fish can strike. In return for their light, the bacteria are rewarded with nutrients as well as protection, so it’s a win for both creatures.
What’s very interesting is that different types of anglerfish are paired with various types of bacteria. Scientists have, as yet, been unable to discover which fish go with which bacteria, but research is ongoing.
Dinoflagellate
Where bioluminescent creatures are concerned, dinoflagellates, also known as fire algae, are potentially one of the smallest. These are single-celled organisms, a subspecies of plankton that are found in almost every type of water. In marine environments, freshwater, and even ice and snow.
Fire algae have earned itself something of a reputation on websites like Pinterest where photos of it lighting up breaking waves and shorelines are in abundance. However, while it is possible to see dinoflagellates like this, sightings of highly concentrated groups are usually only observed in summer. At other times of the year, the fire algae is present but its glow is not strong enough to be seen by the naked eye.
Similar to other bioluminescent animals, dinoflagellates create their glow through a chemical reaction. However, this only happens if the organisms are triggered by something like a change in temperature or movement in the water. It is thought that the light is used to surprise predators and send them running in the opposite direction.
Comb Jelly (Ctenophora)
The comb jelly is a term used to describe more than 150 species and these can be found all over the world but are usually swimming near the surface of the water.
Different species of comb jelly behave in different ways but those that are able to light up do so in one of two ways. Some already contain a glowing chemical compound known as coelenterazine, whereas others have to feed on animals that contain this in order to absorb it into their own bodies.
There are some comb jellies that will flash intermittently to confuse predators while others will release a glowing ink when they are threatened. What’s interesting is that, while the comb jelly actually only glows in green or blue, the way it moves causes it to look more like a rainbow!
Blackbelly Lanternshark (Etmopterus lucifer)
Also known as the lucifer shark, the blackbelly lanternshark uses a luminous patch on its underside in order to confuse prey. Prey are attracted thinking that the shark is much smaller, in a very similar way to the cookie cutter shark we talked about earlier. This clever tactic causes prey to approach and makes it very easy for the lanternshark to feed.
These sharks can be found in temperate or tropical waters and tend to live at much greater depths. While they are often swimming around at just 150 meters, some will dive as much as ten times that.
The way that the blackbelly lanternshark produces its light is through a series of organs within the skin called photophores.
Bobtail Squid (Sepiolida)
Bobtail squids are some of the tiniest, and most adorable squids in the world. They can grow up to 8cm, but it is not uncommon to find them as small as just a centimeter! Owing to this small size, they are sometimes commonly referred to as the stubby squid or the dumpling squid.
Unlike a lot of other bioluminescent animals, the bobtail squid has a rather unique way of lighting up. It has a cavity on the underside of its body where tiny glowing bacteria live. Just like the anglerfish, these bacteria take nutrients from the squid, so it’s beneficial to both parties.
When the bobtail squid is in the moonlight, the cavity will open wider to release the light from the bacteria. There is a flap that behaves as a filter so the level of light can be controlled. In contrast to the moonlight, the bioluminescence makes it much more difficult for predators to spot the squid.
These cute little creatures can be found in the Pacific Ocean as well as some areas of the Atlantic and Indian Oceans. They normally prefer to remain in coastal waters and are closely related to the cuttlefish.
Bigfin Reef Squid (Sepioteuthis lessoniana)
Bigfin reef squids are native to Indo-west Pacific waters and around the northern coast of Australia as well as out to New Zealand. These squids are not actually what we would call bioluminescent but they do create a glow.
However, unlike the other critters on our list, bigfin reef squids use chromatophores, which are packed all over their bodies, to create complex changing patterns. These reflect light in all different colors which give the squid a different appearance depending on the color of the light it is in.
Antarctic Krill (Euphausia superba)
As you will probably guess from its name, the Antarctic krill can be found around the waters of the Antarctic Ocean, often referred to as the Southern Ocean. These krill are incredibly abundant and live in swarms that can contain as many as 30 trillion individuals. These swarms can stretch for up to 12 miles!
While the Antarctic krill plays an important role in controlling the phytoplankton population, it is also a food source for whales who can eat hundreds of thousands of these tiny creatures in a single mouthful. To hide from predators, these animals are bioluminescent. Although, it is important to note that this is only a theory as scientists are yet to discover for certain the true reason for their ability to emit light.
Antarctic krill perform bioluminescence because of complex organs in various locations around the body. These organs can be found on the hips, the eyestalks, and in several other places, and the krill can independently rotate them to emit light in different directions. These organs can be compared to a torch since they feature both a lens and concave reflectors!
