In France, we have to do a group work on a certain subject. Mine is « Why aren’t some bloods red ? » It was really interesting and since I couldn’t help but link it to Homestuck, I thought I might as well share it. 

Please remember that I’m not an expert on the subject and english is not my maternal language, and I’m sorry if I make mistake. If you want, you can do your own research, most of the information is in english anyway.

Let’s start with the basic : our blood and most animal’s blood is red because of hemoglobin, a respiratory pigment (= a molecule that increases the oxygen-carrying capacity of the blood (wikipedia) ) containing iron.

First, I want to talk about Cherubs and their red and green blood.

I discovered a species of lizard that have green blood (and green tissue and bones), even though they have hemoglobin and should have red blood. It is called Prasinohaema virens or green blooded skink. They have a high concentrations of a green pigment, biliverdin. Biliverdin results from the breakdown of the heme moiety of hemoglobin (wikipedia). It normally transforms into bilirubin before being evacuated (bile or urine). The same thing can happen to Cherub, and explain their green blood.

But even if this answer why does Calliope have green blood, it doesn’t answer how they « switch » from one to another. So here is my theory : When they go to sleep, they « adapt » the quantity of biliverdin : they produce it to have green blood or evacuate it to have red blood. But this could leave green blooded cherubs anemic (less hemoglobin). Apart from this, it can work and it strengthen the association between Cherubs and reptiles. 

Troll and their 12-13 blood colors are more complicated, but I still have two theory : 

The easy one : Like Cherubs, they have hemoglobin and alien pigments, which vary in quantities to create the variation of color between castes, and Karkat would be a mutant because he doesn’t have any pigments.

The fun one : Trolls have a lot of different respiratory pigments that gives them their blood colors. (I will only talk about the ones we can find on earth)

-Sea dwellers (and maybe purple blood trolls) would have hemerythrin. It’s a violet-pink respiratory pigment mostly found in marine worms (like magelona or penis worms (maybe this is why most sea dwellers are dicks) ) 

-Blue blood trolls would have hemocyanin (a blue respiratory pigments that uses copper). Maybe some of you know the horseshoe crab : it’s an marine arthropod (not a crab) with blue blood. But, other arthropods like scorpions, spiders (hello Vriska) and even snails have blue blood.

-Green blood trolls would have chlorocruorin (a green respiratory pigment). (I’m not sure about this one because there isn’t much information, and some things are hard to believe) Chlorocruorin is mostly present in worms like christmas tree worms (<== they are really pretty), but some worms species have both hemoglobin and chlorocruorin, and get rid of hemoglobin when growing up. More surprisingly, chlorocruorin seems to be dichromatic and appears green in diluted solution and red in concentrated solution (<== I don’t know if this is true) so Karkat would just be a high-pressure/high-concentration lime blood troll.

-Gold and Bronze blood trolls are a mystery to me (maybe the hemolymph of insects ?)

-Finally, Rust blood trolls would just have hemoglobin, maybe slightly different from human, and more « rust » than red.

Unfortunately, this doesn’t explain why high blood lives longer, or why low bloods have psychic ability, and I’m not sure how most of it would work (especially for trolls), it was mostly for sharing some theories and information.

Fun facts :

-When you lack oxygen, your blood/skin turns bluish, it’s called a « cyanosis ». When cyanide is associated with iron, it makes Prussian blue (almost the same hue as Equius). So, Equius was destined to be strangled.

-The Ice fish doesn’t need respiratory pigments and it’s blood is colorless/white.

-I’m not even a Seer of Blood, just a Maid of Breath really invested in the subject.

In Conclusion :

-Cherubs are skinks

-Trolls are squishy worms

-Limule is a valid troll name (bonus if they’re a blue troll with a horseshoe crab lusus)

-Equius is Prussian

-Fantrolls with colorless/white blood are valid

Thank you for reading it all. Sorry if this was too long, or not clear enough, I’m not the best explainer, but I still hope you learned some interesting things.

I will pass my oral exam on this next week, so wish me luck…

-L

You weren’t kidding, that’s long- And yeah I do recall seeing some posts about Blood Pigments in the past talking about the possibilities with Troll Blood and such! It’s interesting seeing it also applied to Cherubs though, I don’t think I’ve ever seen anyone talk about Cherub Blood, and them being comparable to reptiles makes way too much sense since, you know, snake skeleton angels.

That being said, do we know if Cherubs ONLY have Red and Green? There could be other Cherubs with different blood colors. Who knows really, though.