Why Do Mysterious Lizards Have Green Blood?

Roses are red, violets are blue … and these lizards’ blood is green.

It’s not a trick of the imagination or a penchant for food coloring—Prasinohaema skinks living on the island of New Guinea actually have green blood, bones, and tissue—and one scientist is trying to figure out why.

Prasinohaema skinks are green all over. Photograph by Christopher Austin, Louisiana State University Museum of Natural Science

Louisiana State University biologist and National Geographic explorer Christopher Austin first became interested in these odd skinks in graduate school, when he read a 1969 paper in Science about a strange group of lizards with green blood.

“It immediately captivated my attention. I noticed that no one had really worked on these lizards since then to figure out the what and the why of the green blood,” said Austin, who studied the lizards for his Ph.D. at the University of Texas, Austin. (See pictures of new skinks found recently in the Caribbean.)

Why So Green?

The skinks are found almost exclusively on the island of Papua New Guinea, one of the world’s biodiversity hot spots. (One species can also be found in the Solomon Islands.)

When Austin began studying the animals in Papua New Guinea, he realized they have “incredibly high concentrations of the bile pigment biliverdin,” he said.

Green-blooded lizard's blood compared to typical red blood.
The skink’s blood (bottom) compared with red blood (top). Photograph by Christopher Austin, Louisiana State University Museum of Natural Science

In many species, including humans, oxygen in the blood is carried by hemoglobin, which gives blood its red hue. When hemoglobin starts to break down, it’s transported to the liver, where it’s broken down into molecules such as bilirubin and biliverdin.

These pigmented compounds are excreted with bile into the intestines. Biliverdin has a green hue (you can see the pigment in the greenish areas around a healing bruise), and very high levels of biliverdin in the blood of these skinks is what gives their blood its unusual color. (Also see “Blue Blood Helps Octopus Survive Brutally Cold Temperatures.”)

The green tint isn’t limited to their blood either. “The blood is green, the bones are green, the tissues are green—even their tongue is green,” Austin said.

No other vertebrate is known to have green blood.

Mystery Remains

The remaining mystery, Austin says, is that biliverdin is extremely toxic. If humans have even a tiny amount of biliverdin or bilirubin in their blood, we say that they are jaundiced (their skin takes on a yellowish tone).

Generally this only happens in people with liver damage or in newborns whose livers haven’t yet started to break down old hemoglobin. But if excess bilirubin or biliverdin in the bloodstream goes untreated, it can be deadly.

“It’s surprising because at these concentrations of bile pigments in the blood, [the skinks] should be completely jaundiced, if not dead,” Austin said.

Austin hypothesizes that the lizard evolved to tolerate the biliverdin because it may provide protection against a group of parasites called Plasmodium.

Best known for causing malaria in humans, Plasmodium also causes malaria in reptiles and birds. Austin believes that the presence of toxic biliverdin instead of hemoglobin may make it harder for Plasmodium to infect the skinks. (Also read: “Bedlam in the Blood: Malaria.”)

To answer this question, Austin is currently sequencing the genomes of the Prasinohaema skinks and comparing them with the genomes of closely related skinks that have red blood to identify any genetic changes that could provide resistance to Plasmodium.

Tell us: Why do you think the lizard has green blood?

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Carrie is a freelance science writer living in Virginia. When she's not writing about cool critters, she's spending time outside, drinking coffee, or knitting. You can visit her website at http://www.carriearnold.com
  • kevin munyua

    remarkably interesting.

  • Divya Jyoti Arya

    Maybe, they are venomous! :O

  • David Rechs

    I think the first mutation was a defect in the bile duct. The second mutation, now with a clear survival advantage, was bile tolerance. That the first one happened during a population bottleneck is the surprising thing,

  • Eldon Sarte

    Maybe the excessive biliverdin makes the skinks toxic to predators?

  • Miss_DWilson

    I wonder for what ecological purpose, if not pure coincidence, why these lizards have these bile pigments in their blood? The tolerance of Plasmodium is an interesting idea, but I feel like there’s more to it than that. I’m excited to discover what new research comes of this!

  • James Bryant

    Glancing at the Wikipedia summary on biliverdin, I was surprised to see how many vertebrates exhibit a heightened presence of biliverdin: frogs and fish, but especially in birds and their egg shells (e.g robin’s egg blue). That biliverdin retention is adaptive wouldn’t seem to be a surprise, but the levels it occurs in these skinks is apparently exceptional. Is it possible because they produce so much biliverdin, or because they possess genes for some sort of biliverdin reductase inhibitor? Resistance to Plasmodium alone would seem to be too narrow an adaptation. Perhaps biliverdin is a general augmentation of the immune system in all these vertebrates. Depending on where these skinks live (P. flavipes is apparently found at high elevations in New Guinea) they may need to use biliverdin to make up for what they don’t get in sunlight energy and general body warmth.

  • Joe Smith

    The blood will blend in with their skin so when they’re harmed they have less chance of being noticed because of it.

  • M harris

    That is a great and strange news.I like it.That is an alien lizard. 🙂

  • Ronnie Ephraim

    another great findings

  • Soumendu Das

    Fascinating to know how these creatures had evolved themselves to such high level of biliverdin! However, would like to know what exactly turns these creatures’ bones green… 😮

  • Katherine Kay Mariano

    The explanation above already sounds convincing. But maybe the green color (of the lizard’s body) also helps it to camouflage against other predators?

  • Robert C Brooke

    Could the high levels of biliverdin make them unpalatable to predators?It seems this could be a fringe benefit of being able to tolerate high biliverdin levels.

  • Phillys

    I would hazard a guess that the bones turn green for the same reason some birds’ eggs are blue/blue-green: because the biliverdin “stains” them that color.

  • Cheyenne

    Clearly the population of skinks with the mutation causing green skin was able to survive malaria more often than their normal relatives, without deleterious effect. This allowed the green-blooded skinks to reproduce more often, so they continue to this day.

  • j miller

    my guess that having biliverdin in thier system might very well be an adoptive defense mechanism that has been developed over evolution. For skinks to be harmful to humans i could only imagine what the effects would be on other species. however, another outlook could be from adoptivity through surroundings

  • Mr Carl

    The lizards arms look feeble is it a weak animal that could be preyed on by birds in a location with lots of high grass? It could be a camo adaptation.

  • Tarun

    Its really strange. this type of fact force to believe, that how unknow we are about Mother Nature!

  • mwills

    Maybe it eats only green bugs

  • L M Bowland

    Perhaps developing a defense against malaria came first but developed into a defense against predators as well? It wouldn’t take long for the average predator to learn ‘Don’t eat the green ones, they’re poison’.

  • brandon sipe

    God made them special and he made their blood green for a reason

  • Raees

    It’s fascinating how much we can still learn from our environment. Evolution has truley made many creatures unique and fun to learn about.

  • John Jones

    I have one of these lizards at home.

  • Mark

    It’s obvious why they have green blood. They’re from Vulcan.


  • Dwayne LaGrou

    I think they have green blood because they came from the planet Vulcan, Just like Spock!

  • Diane

    Frequencies…all light and color is frequency…

  • Robert Rensch

    Is the blood the same color when depleted of oxygen? Maybe this guy has copper based hemogloben like Mr. Spock… Copper oxide is, of course, green.

  • Defiant

    Read about octopi the other day…learned that, like Vulcans (LOL!) their blood is based on copper instead of iron…and as a result, is green instead of red. Different reasons from the skinks, but interesting.

  • peter James

    There are no restrictions to evolution. If green works so be it. Chlorophyll is the blood of life for many plants. Why can’t a reptile adapt to it as well as a plant.

  • faisal

    what is this

  • prasannjit

    will have to look at these places of mysterious lizards and see if malaria is prevalent.then only we can say that it ‘evolved’ itself.

  • Patrick Okey

    Is interesting, but i think that the bile pigments may not
    be as toxic as that of red blooded organisms & possibly
    playing the role of hemoglobin as in red blooded.

  • Lalan Prasad Shah

    Dear, Sir!
    It is an important discovery, but it needs much works, so wish for ur success!

  • James Grant

    All the raptilians are green inside out because they were made by SATANS of pakisatan who are know worldwide as Pisslamiq Terrorbeasts.

  • M.D. Thomas

    Human bones are pinkish until they dry out because our red blood is produced in our marrow. The PH base of bile secretions is pretty acidic and has an even greater enzymatic penetration and “staining” quality than oxidizing iron. Having blood that is resistant to Malaria is a huge evolutionary advantage, and, it would make the skinks very unappetizing or even poisonous to it’s natural predators.

  • farang

    Why does the lizard have green blood. As an evolutionary defense mechanism against Malaria infection sounds good to me.

  • Christian Leonard

    Maybe its some kind of Toxic type of lizard and the source it the tissue, blood, etc.

  • El Gabilon

    This skinks blood is not green, it is tinted green which is far different than being green. It has probably evolved in such a way as to protect itself from its enemies. In humans some have blue tinted blood which is caused by an over indulgence of blueberries over time. Some who work with roses have body odor that smell like roses. Our question is if the mystery still remains why was a Phd granted for this study? Are Master and Phd degrees to easily attained these days?

  • Mark O’Shea

    If you get the chance to check it out look for my film “Green Blood” on Animal Planet/Discovery, a film in the second season of O’Shea’s Big Adventure in which Chris Austin and I visited PNG to look for Prasinohaema skinks, take blood samples and investigate this phenomenon. Like Chris I was fascinated by these lizards, from the 1969 Greer & Raizes paper on their biliverdin blood pigment which I read when I captured specimens on two species (from the five known) of Prasinohaema during fieldwork in PNG in 1986. My initial thought was that the biliverdin pigment may make the lizards distasteful to their predators but we discovered they are eaten by birds which have no taste buds so that theory fell apart. Chris had the theory about antimalarial protection and that made a lot of sense as there are 7-8 lizard malarias compared to five humans malarias. This is indeed a very interesting story and I am pleased to see it in the news again.

  • Julian

    “No other vertebrate is known to have green blood.”.

    The Garfish is a vertebrate that also has green blood, also due to biliverdin. see http://en.wikipedia.org/wiki/Garfish

  • Julian

    RE; The Garfish, sorry my mistake. It has green bones due to biliverdin, but not green blood.

  • William

    Maybe it has something to do with their diet? Like when humans eat many carrots they turn green. There diet may be taken to an extreme level. It could possibly be part of their genetics, check their chromosomes, and what it looks like inside the skink as a baby.

  • Harry Mikolowski

    I believe that the reason that these skinks have green blood is because everything that GOD makes is complete & mature.
    there is no scientific evidence to describe GOD’s holiness and love. If I may give an example of a supposed quote on quote missing link is the archaeopteryx a supposed proof & ancestor of how dinosaurs evolved into birds, mainly because of it’s teeth that was in it’s beak & also the fact that it claws on it’s wings. Just in case you people didn’t know is that the South American Hoatzin when it is just a hatchling also has claws on it’s wings , does this that also another missing link that is between dinosaurs & birds, NO- it just means that young hoatzin needs the claws on it’s wings so that when it is learning to fly & if it falls to the ground it can climb back up to it’s nest, so that it doesn’t become some other creatures meal. two-three other birds that have claws on their wings as well as the hoatzin are ostrich, emu cassowary. If you have any questions I will be willing to answer them to the best of my ability.
    Your’s in Christ Jesus, Harry Mikolowski

  • xenopus girl

    Biliverdin has been shown to be a protease inhibitor.
    So I was wondering if you are on the right tract with biliverdin being a defense against pathogens, but perhaps you are focusing on the wrong pathogen. i.e.is the pathogen being protected against a virus and not malaria.

    Relating to the idea of this being part of an immune response, I have the following question: are Biliverdin concentrations constant in a given animal at all times, or do they change? The reason I ask, in so called warm blooded animals, body temp is increased in response to infection. If you are proposing that Biliverdin might be a defense against protozoa or viral infections one might expect it to increase in response to infection.
    You could probably come up with a simple experiment to determine this.

  • Croft the Great the Third of Cornwall

    You know, people are giving all these science answers when the real one is simple: they’re actually aliens trying to observe our planet for the invasion. The end is nigh!

  • Abraham Santoyo

    Why are we all sticking to one hypothesis, the creatures may have developed all of these defenses, coper concentrations for a certain purpose, maybe for many purposes, and please stop with the god stuff ok I have read the first testament twice and part of the first. The first testament speaks of unicorns, and not kidding, dragons in Reveation 20:1-15, Satan is depicted as a serpent like dragon, and then is thrown into the bottomless pit. So please stop trying to bring God up in a scientific discoshon. Also my birthday past on October 6, 2014, I’m finaly 15, yay!

  • simon opeyemi

    Incredible……but Ȋ̝̊̅ quess dis has to do with skinks heart than the acclaimed biliverdin…since all blood comes frm the heart….wish to see this creature…weldone mr austine….

  • Mary Anne Clark

    Does somebody know if biliverdin itself really is toxic in reptiles? The two medical books I’ve read on this topic say that it is not — it’s the bilirubin that the biliverdin is converted to in mammals that is toxic, and that most reptiles and birds do not make that conversion. So is there evidence that the biliverdin itself is toxic to reptiles or birds? These lizards seem to be tolerating it well.

  • Christopher Pacheco

    You know some scientists believe that dinosaurs had the same attribute. There are also ancient Sumerian stories of Tiamat creating or embodying reptiles with poisonous blood to avenge the death of Abzu at the hands of her offspring.

  • ColdFusion

    Huh, that’s one way to prevent malaria I guess. I wonder, between this and that whole sickle cell thing, which is worse

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