Warning: This is a bloody article. Not suitable for people with homophobia.
Is Blood Red or Blue?
It is a common sense that blood is red. However our blood appears blue when we look at our veins. Is blood red or blue? In case you have not seen human blood before, blood is actually red due to the hemoglobin protein in the blood. The hemoglobin protein is consisted of hemes subunits which bind with iron molecules. When the iron molecules on the hemes interact with oxygen, red colour is produced from these oxygen-rich blood. What makes the vein appears blue on your skin is due to the wavelengths of the light reflected from the skin. The blue light just can’t penetrate the skin deeper than red light, hence the veins appear blue.
Since human blood is red, can we assume all animals have red blood? No! Do not be shocked if you see any animals with non-red blood, and they are not alien to this planet. Below is the list of animals with blood of other colours.
Animals with Blue Blood
Unlike human blood which is iron-based, there are animals with copper-based red blood. The blood of these animals does not contain hemoglobin. Instead they have hemocyanin which helps to carry oxygen to cells. There are many pharmaceutical value in blue blood due to its unique chemical properties, such as bacterial toxins detection and cancer vaccines.
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Horseshoe Crab (blue blood)
Horseshoe Crabs are living fossils which can be date back over 450 million years. That means they existed before the age of dinosaur. They can be found in North America and Southeast Asia. Horseshoe crabs have strange anatomy which does not resemble the crabs we know. This is because Horseshow crab is not a real crab at all. In fact, horseshoe crabs is classified under the subphylum Chelicerata which also contains scorpions and spiders.
Today, horseshoe crabs are blue chip to the biomedical industry. Since researchers discovered the copper-based blue blood of the living fossils clotted when exposed to E. coli bacteria in 1971, pharmaceutical companies have been harvesting horseshoe crab blood for the chemical amoebocytes in the coagulogen cell. The chemical is only found in horseshoe crab blood. Amoebocytes are used to detect dangerous bacterial endotoxins in human medication and in medical tests. Today, horseshoe crab blood is priced at an estimated $15,000 per quart.
Octopus (blue blood)
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Blue blood is not limited to creatures with hard shell. Octopus which has no protective shell has blue blood too. Same as horseshoe crabs, octopuses’ blue blood also contains hemocyanins which oxygenate their bodies. The blue blood pigment helps the octopuses to survive in cold harsh environments, especially at Southern Ocean surrounding Antarctica, in which the temperature ranges from -1.8°C to +2.0°C. The blue blood does not restrict octopuses live at cold environment. The blood actually works better in transporting oxygen when the temperature of the water is warmer.
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Cuttlefish (blue blood)
Other than blue blood, cuttlefish has three hearts. Two of the hearts are used to pump the blue blood the gills (the lung) for oxygen absorption, whereas another one is used to pump blood into other organs. Cuttlefish usually appear near the seabed in search for mollusks and small fishes as food. Despite having blue blood, cuttlefish has the ability to change its skin colour and texture for perfect camouflage.
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Pillbug (blue blood)
Although many think of “blue blood” as nobelty and royalty, pillbug may not fit into that description. Some of you may not be familiar with pillbug, perhaps one of these names will ring a bell – roly poly, wood louse, armadillo bug, potato bug. Pillbug is called roly poly because it curls into a tight ball when felt threatened. While it is perfectly normal to pillbugs, human will tend to feel disgusted when they find out pillbug can drink with its anus and eat their own poop. All these lowly characteristics do not kick pillbug out from having blue blood. However if you see a bright blue pillbug, it does not mean that the pillbug is reflecting the colour of the blood. It simply means that the pillbug has viral infections. Do you know that pillbug is not a bug, but belongs to the family of shrimp and crayfish?
Tarantula (blue blood)
Blue blood is not exclusive to marine animals only. Tarantula, a hairy spider also has blue blood. There are 900 species of tarantula has been identified till this date. Tarantula’s blood is known as hemolymph which is different from mammals’ blood. Hemocyanin in hemolymph makes it appear clear to blue in colour. Tarantula controls the flow of hemolymph with heart pumping initiated by nerve cells to all parts of the body. As tarantula does not have blood vessels and it uses open passages for blood flow, it prevents tarantula from bleeding to death when it loses its leg (a common health concerns to the hairy spider). When a tarantula breaks its leg, the hemolymph will dry up (similar to human’s clotting system) and will begin to regenerate a new leg when it starts to molt. Can you guess out other names of tarantula? The giant hairy spider often known as baboon spider in Africa and monkey spider in South America.
Clam (blue blood)
Cockles (blood clams), which are usually prepared as a Chinese delicacies, appear red due to high hemoglobin liquid, but other clams possess blueish liquid in their body. However clams’ hemocyanin oxygenate, it will turn into oxygemocyanin and lose its colour.
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Emperor Scorpion (blue blood)
One of the biggest scorpions in the world also carry blue blood in its black body. Emperor scorpion (Pandinus imperator) has the blueish hemocyanin protein which binds oxygen between two copper atoms. Due to its less poisonous venom than other scorpions, many people keep emperor scorpion as pet. However, its venom can be potent to people who are allergic to it. The blue-green glow of the emperor scorpion under ultra-violet light is not due to the blueish protein in its blood. The emperor scorpions use the protein in their exoskeletons to convert UV light into a light with blue wavelengths.
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Snail (blue blood)
Snail being one of the mollusks also have blue blood. With the exception of ramshorn snail (freshwater snail) which has red hemoglobin in their blood, other snails’ blood contain hemocyanin. In recent years, there was a hype on harvesting a sea snail (keyhole limpets) which fetch up the blue blood value to $900,000 per gram due to its potential to be cancer vaccines. Currently the keyhole limpet blood is harvested by a biotechnology company in California, Stellar Biotechnologies.
Lobster (blue blood)
The red lobsters on your dining table will never give you a clue that it has blue blood. Even when you are slaughtering that those lobsters in the kitchen, you will not see blue blood spilling all over the kitchen as well. Similar to clams, lobsters’ blood convert into clear blood due to oxygenation when hemocyanin comes in contact with oxygen.
Squid (blue blood)
What are the differences between octopuses and squids? They are both members of cephalopod class with a prominent head and a set of tentacles. Octopus’ head tends to be round and have eight arms, whereas squids have triangular shaped head, two fins, eight arms and two tentacles. They also produce different coloured inks. Generally squids produce blue-black ink and octopus ink is black. One of the common thing both marine animal share is copper-containing blue blood.
Animals with Yellow Blood
What we are going to show you next is animals with yellow coloured blood. Yellow blood is consisted of yellow vanadium-based protein known as vanabin. Although hemovanadin is a blood, it does not have the function of hemocyanin and hemoglobin as oxygen carrier. When hemovanadin is exposed to oxygen, the blood will turn into a mustard yellow.
Sea cucumber (yellow blood)
Sea cucumbers are not plant. They are marine animals commonly found on the sea floor worldwide. Sea cucumbers are also used in various cuisines and medicinal application. 10% of sea cucumber’s blood is vanadium. The yellow blood cell pigment gives them yellow blood.
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Sea squirt (yellow blood)
One marine creature that has interesting name would be sea squirts. The creature squirt out water when they are remove from water. Sea squirts come in various shapes, including sponges, grapes, and rubbery blobs. Sea squirts accumulate high concentration of vanadium which make its blood yellow. It is fascinating how sea squirt is able to accumulate vanadium as it is scarce in sea water.
Animals with Green Blood
In 2007, a Canadian man shocked his surgeons for having green blood through his arteries. After analysis, it was found out that sulphur atoms were incorporated into hemoglobin and caused sulfhaemoglobinaemia. This happened likely due to excess intake of sulfonamides. However, green blood is not so straight forward. Sulfhaemoglobinaemia or sulfhemoglobinemia is only a rare blood condition of human which is usually drug induced. How did animals get their blood green?
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Green Tree Skink (green blood)
One way to get green is having excess biliverdin, which is a green tetrapyrrolic bile pigment which is sometimes found in bruises. Green Tree Skink (otherwise known as green green-blooded skink) is a lizard species of Prasinohaema genus native to New Guinea. As a result of excessive biliverdin, green tree skink has green muscles, bones, tongue and other green body parts. It is amazing as the level of biliverdin in green tree skink is toxic if the same amount is in other vertebrates.
Marine worms (green blood)
The protein chlorocruorin will also makes blood green. Many marine worms (such as tubeworms) contains chlorocruorin in their blood plasma which is used to transport oxygen. In a diluted amount of deoxygenated chlorocruorin, the blood will be in light green colour but appear light red if it is in concentrated amount. The colour of chlorocruorin will change to darker green when expose to oxygen. Annelids (such as earthworm and leeches) also have green blood.
Animals with Pink/Violet Blood
Another alternative of oxygen carrier in blood is hemerythrin protein. Although hemerythrin is also iron based, its structure is different from hemoglobin which leads to different colour formation when expose to oxygen. The respiratory pigment will turns pink or purple when oxygenated. As hemerythrin is a reversible oxygen carrier, it is less efficient than haemoglobin.
Magelona (pink/violet blood)
Magelona is a single annelid worm (ringed worm) genus which has pink blood. Magelona of North America has pale violet blood, whereas magelona species from the North Atlantic has pink blood.
Peanut worm (pink blood)
Peanut worm is a species of Sipuncula (unsegmented marine worms). The pink fat worms are usually found in mangroves, muddy soft ground or sandy areas near seagrasses. Just like other sipunculans, peanut worms do not have a vascular blood system. It has coelomic fluid containing hemerythrin which gives it pink blood. It is usually collected as duck feeds in Singapore.
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Penis worm (pink blood)
The worm got its obscene name due to its shape resembles the shape of human penis. It is a priapulida phylum of marine worms. The worms can be found in mud as their main food is mud. Penis worms also do not have a vascular blood system. It also does not have respiratory systems. However it has space containing cells with respiratory pigment hemerythrin.
Brachiopoda (pink blood)
Another marine invertebrates which has hemerythrin is brachiopods which are found in cold water. This marine animal looks like clams, but they are different in their anatomy.
Animals with Transparent Blood
After knowing there are different blood colours, you might still be surprised to find out that there are animals with colourless blood. The science behind crystal clear blood is very simple as these animals do not have any respiratory pigments in their blood.
Crocodile icefish (colourless blood)
One might interpret from the name that crocodile icefish is a type of crocodile that lives in icy cold seawater. Crocodile icefish does live in low water temperatures of -1.8°C to +2.0°C of Antarctica (same as the octopus with blue blood). It was discovered by a biologist named Ditlef Rustad in 1928. Due to its crystal clear blood, crocodile icefish is also known as white-blooded fish. It does not use hemoglobin to transport oxygen to any part of the body. Instead, the fish dissolve oxygen into blood plasma and move them around the body.
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