Bleeding Rainbow

by Dr. Gordon Wilson on January 1, 2022
Featured in Answers Magazine
Audio Version

In God’s vibrant creation, even blood comes in different colors.

Green blood coursing through the veins of Vulcans may seem out of this world, but real green blood was around way before Spock beamed aboard the starship Enterprise. Sometimes science fact surpasses science fiction.

We’re very familiar with the red blood found in humans and most vertebrates. But God loves variety. In addition to making many different animals, he even designed their blood in a striking palette of colors—of course red, but also orange, yellow, green, blue, and violet-pink to purple. Some creatures even have clear blood. Each kind of blood is specially designed for a particular function within these colorful creatures.

As we ponder the extreme differences among God’s creation, it’s no big surprise to find blood of different colors. It should prompt us to praise our Creator for his infinite wisdom on display in the hidden details of creatures great and small.

“Great are the works of the Lord, studied by all who delight in them” (Psalm 111:2).

Red Blood

With a few exceptions, vertebrates (fish, amphibians, reptiles, birds, and mammals) have red blood thanks to a protein called hemoglobin. Each hemoglobin has four iron-containing molecules called heme groups, each of which can carry one oxygen molecule. Therefore, one hemoglobin can carry four oxygen molecules.

Just one human red blood cell has around 250 million hemoglobin molecules. So that means one red blood cell can carry about 1 billion oxygen molecules. And one drop of blood contains about 250 million red blood cells. All that iron adds up, making vertebrate blood very red. Whether oxygen is picked up by the bloodstream at the gills, lungs, or skin, hemoglobin is the red molecular taxicab that carries oxygen to all the tissues in the body.

Orange Blood

Like other insects, female cockroaches have clear blood. However, the fat body (an insect organ similar to the liver) releases orange proteins (vitellogenin) into the hemolymph, tinting it a light orange. Vitellogenins are converted into yolk proteins in their eggs.

Yellow Blood

Some beetles, sea squirts, and sea cucumbers have yellowish blood due to vanabin, a protein that contains the metal vanadium. Contrary to previous assumptions, scientists doubt that vanabin carries oxygen in the blood because many sea squirts also have hemocyanin, assumed to be the oxygen carrier. Perhaps the vanabins are present because they are toxic to microbes, parasites, and predators.

Green Blood

Green-blooded worms are found among some marine polychaetes (a group of marine segmented annelid worms). These have a green pigment called chlorocruorin that transports oxygen, similar to hemoglobin.

The green-blooded skink, a lizard, has high concentrations of the green bile pigment biliverdin (a breakdown product of hemoglobin) that would be quite toxic to other vertebrates. Bile pigments are normally secreted into the digestive tract to break down fats. But though they build up in this lizard’s bloodstream to astonishingly high levels, the lizard doesn’t go green around the gills (or experience any other adverse effects). Although the lizard has normal red blood cells with oxygen-carrying hemoglobin, the abundant biliverdin overpowers the red pigment with green. Some scientists suggest that biliverdin may provide protection against disease.

Violet Blood

The protein hemerythrin colors some animals’ blood purple. Hemerythrin transports oxygen in the bloodstream of brachiopods (mollusk-like invertebrates) and several marine worms (peanut worms, priapulid worms, and one genus of annelid worms). Though clear in the creature’s body, this protein turns a lovely violet-pink or purple color when oxygenated.

Blue Blood

“Blue blood” figuratively means a person of noble birth. But the blue bloods we’re talking about aren’t superior to other invertebrates. Their blood is literally blue. Certain mollusks like clams, snails, slugs, octopuses, squids, and certain arthropods like horseshoe crabs, lobsters, and spiders have a metalloprotein called hemocyanin. Like hemoglobin and hemerythrin, hemocyanin transports oxygen in the blood. But unlike hemoglobin, hemocyanin is not contained in blood cells, but rather transports oxygen freely in the blood of these arthropods.

Embedded in the structure of hemocyanin are two copper atoms carrying one oxygen molecule. The copper atoms turn a pretty shade of blue when bound to oxygen.

Clear Blood

Most insects don’t need red blood cells because their blood, called hemolymph, isn’t designed to transport oxygen and carbon dioxide. Instead, they have a network of tiny airways like our respiratory system. But they don’t use these airways to deliver oxygen to the lungs—insects don’t have lungs. Rather, their whole body is like a lung. Atmospheric air is piped throughout their entire body, so all their tissues receive oxygen directly from the air. With that kind of ventilation, who needs hemoglobin? Instead, their hemolymph transports nutrients, hormones, and everything else that normal blood carries.

Dr. Gordon Wilson, Senior Fellow of Natural History at New Saint Andrews College, earned an MS in entomology from the University of Idaho and a PhD from George Mason University in environmental science and public policy. He narrates the nature documentary series The Riot and the Dance and is the author of A Different Shade of Green.

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January–March 2022

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