Do All Animals Have Red Blood?

(hint: nope. BIG nope.)

What IS blood, anyway?

Welcome back to school, my cheeky monkeys! In today's Keating Creature newsletter we're getting messy and talking about BLOOD. You already know what blood is, and I'm sure you've all seen your own blood too. It's the stuff that oozes out of you when you get a papercut. It's also the stuff that gets everywhere if you are ever unlucky enough to get bopped on the nose with a soccer ball. (I do not recommend this.)

But do you know what blood actually is? Blood is nature's way of making sure we have oxygen everywhere we need it in our bodies. And like everything else in our bodies, blood needs to be MADE. Yup, the same way you need ingredients to make a cake, you ALSO need ingredients to make blood. Only to make blood you don't need an oven, you just need bone marrow. That's where you're blood is made!

Recipe for Blood

(walnuts optional)

To make blood, your body needs to use four main ingredients:

  • white blood cells (these things fight infections!)
  • red blood cells (the cells that carry oxygen all over your body)
  • platelets (these are the reason you stop bleeding when you get a cut)
  • plasma (a yellowy liquid that helps carry proteins and other good stuff throughout your body

Put all of these together and you get the blood that circulated all through your body!

Human Blood is RED... but what about other animals?

Red Rover, Red Rover, Let Oxygen Over!

Human blood is red because of a protein called hemoglobin, which acts like a suitcase for oxygen, carrying it all around the body. The fancy name for a molecule that does this is respiratory pigment. Different respiratory pigments create blood with different colors. When hemoglobin is carrying oxygen with its pal iron, it appears red! This is the color you're seeing when you get a papercut.

But what about animals who DON'T have hemoglobin in their blood?


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Prasinohaema (say what?!)

Although it seems straight out of a sci-fi novel, blood can also be green! In fact, there is a whole group of skinks that bleed green. Their genus name is "Prasinohaema", which is greek for "green blood". These skinks have green blood because of a buildup of a liquid called bile. (You have bile in your body too, but not enough to make you turn green.)

FUN FACT: This bile is also one of the reasons lizards taste disgusting. It's a good way to keep predators from wanting to eat you!


A Lobster, an octopus, and a crab all walk into a bar...

You know how hemoglobin carries around oxygen in our bodies? In lobsters, octopuses, and horseshoe crabs, the job of hemoglobin is done by a different molecule, called hemocyanin. This molecule likes to hang out with copper while it carries oxygen around the body, which makes their blood blue! Both human blood and lobster blood does pretty much the same thing, but how cool would it be to have blue blood, right?!
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Note: Spock's* Blood

According to the internet, Spock's blood is blue-green, too. I can only guess that this is because Spock also has hemocyanin and copper in his blood! Those Vulcans are tough cookies, after all.

(*It is also important to note that Spock is fiction. Sorry.)


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Now, beetles don't have actual blood like us (they don't even have blood vessels!) But beetles DO have a gooey plasma inside of them that keeps them alive, carrying nutrients and proteins all over their bodies. If you've ever squished a beetle (or seen one splatter against your car windshield), you've probably noticed they're insides are a barfy yellowy color. This color comes from that plasma inside of them, which doesn't have hemoglobin. (Just don't go squishing bugs to see it!)

FUN FACT: Insect blood is called hemolymph.

CRYSTAL CLEAR? Meet the Crocodile Icefish!

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(also known as "The One They Thought was a Hoax"

Scientists were so used to learning about respiratory pigments that when they discovered the crocodile icefish, they seriously thought it was a joke. What's so weird about this guy?

The icefish has NO respiratory pigment. None at all. It's blood is colorless, and they don't use any special molecules to carry oxygen around their bodies. How do they survive? Icefish are lucky to live in the very cold waters of Antarctica (there is more oxygen in cold water!), so it can absorb lots of it through its skin. They also don't move very fast, so they don't need as much oxygen as other fish. Being lazy comes in handy sometimes.

If you could have blood of any color, what would you choose?

Fancy Words to Know:

  • bone marrow: a thick, spongy jelly inside your bones

  • hemoglobin: an oxygen-carrying pigment in red blood cells

  • respiratory pigment: a protein that carries oxygen throughout the body

  • hemocyanin: a respiratory pigment that contains copper, found in some arthropods and mollusks

  • hemolymph: the circulatory fluid of insects

Thanks for Reading!

I'm a zoologist turned children's book author!

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