January 27, 2026 • 10 mins
Not all animals have red blood -- it can also come in green, blue, clear, and even dichroic varieties. Learn more in this episode of BrainStuff, based on this article: https://animals.howstuffworks.com/animal-facts/5-animals-whose-blood-isnt-red.htm
See omnystudio.com/listener for privacy information.
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Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio, Hey brain Stuff
Laurin bolabahm here. Red elicits strong reactions around the world.
It is by far the most commonly used color in
national flags. It can be a major confidence booster. Researchers
have found that wearing red garments makes people feel more attractive.
(00:26):
On the flip side, according to one study from twenty thirteen,
looking at red things might cause us to experience pain
more intensely. Maybe red wouldn't provoke our brains so much
if it didn't happen to be the color of human blood.
In this regard, Homo sapiens is far from unique. From
timberwolves to tiger sharks, most vertebrate animals have crimson colored
(00:50):
blood in their veins. This hue is produced by hemoglobin,
the protein that helps our blood distribute oxygen around our bodies.
Read school, you probably learned that blood contains three types
of cells. White blood cells help us fight off viruses,
harmful bacteria, and other pathogens. Then we've got platelets, the
(01:10):
damage control specialists that allow our blood to clot. A Last,
but certainly not least, we've got red blood cells. Their
main purpose is to carry around oxygen from and take
away carbon dioxide to the lungs, where these gases are
inhaled and exhaled, respectively. The protein hemoglobin lets these cells
(01:31):
execute both tasks, a core ingredient in red blood cells,
hemoglobin combined to oxygen and carbon dioxide. Hemoglobin is partly
made up of iron atoms, which give this protein, and
by extension, are red blood cells a crimson color. Since
our platelets and white blood cells are vastly outnumbered by
(01:52):
red blood cells, human blood as a whole looks red,
but like many things, blood exists on a spectrum due
to the pressures of evolution. We've got everything from blue
blooded invertebrates to green blooded reptiles to fish with transparent
fluids in their veins. Today, let's talk about some of
(02:13):
the curious critters with blood in colors other than red.
First up, New Guineas green blooded skinks. New Guineas home
to multiple lizard species from the skink family that have
line green blood. Consequently, their tongues, muscles, and bones are
all various shades of green. Like humans, reptiles have hemoglobin
(02:36):
rich red blood cells, but such cells do not live forever,
and when they break down in our bodies as well
as the lizards, a green pigmented waste product called biliverdin
is created. Most vertebrates filter this stuff out of their
circulatory systems because excess biliverdin can harm cells, including neurons
(02:56):
and DNA. These lizards have a level of verdin in
their veins that would kill a human. Moreover, the pigment
is so densely concentrated that it overrides the hemoglobin and
makes their blood look green. Herpetologists aren't entirely sure why
these lizards possess this trait, but it's apparently a strong one.
(03:18):
In a study published in twenty eighteen, researchers carried out
a genetic survey of fifty one different skinks in Australia, Asia,
and the Islands between them. They analyzed six of the
green blooded New Guinea species in the process. It turns
out that those biliverden loaded reptiles aren't even closely related
to one another. It seems that each of them is
(03:40):
descended from red blooded ancestors, and they evolved green bloodedness independently.
Such an unusual trait wouldn't have evolved six times over
if it didn't offer some kind of benefit. But again
we're not sure what it is. Predators that eat the
lizards don't get sick afterward, and the skinks are no
better camouflaged than their red blooded cousins. It's possible that
(04:04):
the special blood helped their ancestors kill parasites, but more
research will be needed to confirm or refute this. While
we're waiting on that, let's move on to the crocodile
ice fish, so named for their long toothy snouts. The
sixteen species of crocodile ice fish that have been recognized
all live in the ocean waters around in Arctica. These
(04:27):
extremophiles are built to thriving conditions that would kill most
other vertebrates. They frequent brutally cold areas where the water
temperature can plummet all the way down to twenty eight
degrees fahrenheit or negative two celsius. That's below the point
at which freshwater freezes. In such cold water, red blood
cells turn into a liability. That's because blood with the
(04:50):
high percentage of these cells becomes dangerously thick and hard
to circulate when the temperature gets too low. A fish
that thrive in cold waters tend to have proportionately fewer
red blood cells than their warm water counterparts do. But
crocodile ice fish take this to the extreme. Unlike every
(05:10):
other known type of vertebrate animal, they don't have any
red blood cells or hemoglobin at all. Now you might
be thinking, wait a second. Without hemoglobin or red blood cells,
how do the fish circulate oxygen through their bodies. To
get the job done? They enlist the ocean itself. Cold
(05:30):
water is naturally richer in usable oxygen than warm water.
Crocodile ice fish absorbs above this oxygen directly from the
ocean around them and send it into their blood streams.
The blood itself is a colorless liquid, a fact that
really surprised the biologists who discovered these fish in nineteen
twenty eight. It turns out that this cold water oxygen
(05:52):
is so abundant that, upon absorption, it doesn't need to
hitch a ride on red blood cells to get around. Instead,
it can travel from point A to point B inside
the fish's plasma hemoglobin free. But okay, As so far
we've been talking about vertebrate animals, which nearly all use
hemoglobin to circulate oxygen. Many invertebrates use an alternative protein,
(06:16):
hemocyanin both are capable of binding to and transporting oxygen.
But whereas hemoglobin contains iron atoms, hemocyanin incorporates copper. As
a result, blood containing hemocyanin looks markedly different from our
human blood. When hemocyanin rich blood becomes oxygenated, the copper
(06:37):
in it turns it blue. The list of invertebrates that
rely on hemocyanin instead of hemoglobin is a long one,
including crustaceans, spiders, and scorpions. The roster also includes certain mollusks,
like everyone's favorite multi armed brainiacs, octopuses. Yes, octopuses have
literally blue blood and three hearts with which to pump
(07:01):
it in oxygen poor deep sea environments, hemicyanin is better
than hemoglobin, carrying that precious oxygen through in animal's veins.
Octopuses use the protein to stay alive in some seriously
deep waters and at a wild range of temperatures, from
what would be below freezing in fresh water to superheated
(07:21):
near thermal vents. Additionally, hemicyanin helps these tentacled critters regulate
the salt content of their blood so that it matches
that of the water that they're swimming. In next up brachiopods.
These are ocean dwelling animals that resemble clams, though they
evolved independently. Braccupods grow a pair of shells around the
(07:44):
upper and lower surfaces of their squishy bodies, connected with
a hinge at one end, a found in an assortment
of marine habitats. The creatures filter tiny food particles out
of the water. Although there are over three hundred living species,
most people is so brachiopods with prehistoric times because these
hard shelled creatures are disproportionately well represented in the fossil record.
(08:08):
Extant brachiopods do not rely on either hemoglobin or hemocyanin
to ferry oxygen in the blood. Instead, they have heemerthrine,
yet another pigmented protein. Like hemoglobin, it contains iron atoms,
albeit in a different arrangement. Heemerythrine makes deoxygenated blood look colorless,
(08:29):
too faintly yellow. Once the blood starts taking on oxygen,
it adopts a violet, pinkish hue. You'll also see this
kind of blood in marine worms in the class Sypuncula.
They're nicknamed peanut worms because some of them have bodies
that grow in small pointed ovals, looking a bit like
shelled peanuts. These buddies often reside in shallow waters, burrowing
(08:54):
in sand or mud, or taking up in crevices or
unoccupied shells. Other ocean going worms have a different circulatory setup.
If a diver were to spot a live polyket cruising
through the waves, they might mistake it for a sentient
feather duster. Most of these worms are covered in bristles
(09:15):
and tentacles, whose function varies from species to species. Some
have red blood, but others harbor green blood. The latter
use the oxygen binding protein chlorocrurine in place of hemoglobin.
It also uses iron to bind to oxygen, but in
yet another formation, it's what's called dichroic, or too colored,
(09:39):
which means that it can appear to be different colors
in different circumstances. When chlorocrurine is concentrated, its molecules stack
to appear deep red brown, but when it's dilute it
appears green, which means that even if Kermit was right,
and it's not easy being green, at least those new
(10:00):
guinea skinks have some creepy Crawley Company. Today's episode is
based on the article Five Animals whose Blood Isn't read
on HowStuffWorks dot Com, written by Mark Mancini. Brain Stuff
is production of iHeartRadio in partnership with HowStuffWorks dot Com
and is produced by Tyler Klang. Four more podcasts my
(10:22):
heart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever
you listen to your favorite shows.
Welcome to Brainstuff, a production of iHeartRadio, Hey brain Stuff
Laurin bolabahm here. Red elicits strong reactions around the world.
It is by far the most commonly used color in
national flags. It can be a major confidence booster. Researchers
have found that wearing red garments makes people feel more attractive.
(00:26):
On the flip side, according to one study from twenty thirteen,
looking at red things might cause us to experience pain
more intensely. Maybe red wouldn't provoke our brains so much
if it didn't happen to be the color of human blood.
In this regard, Homo sapiens is far from unique. From
timberwolves to tiger sharks, most vertebrate animals have crimson colored
(00:50):
blood in their veins. This hue is produced by hemoglobin,
the protein that helps our blood distribute oxygen around our bodies.
Read school, you probably learned that blood contains three types
of cells. White blood cells help us fight off viruses,
harmful bacteria, and other pathogens. Then we've got platelets, the
(01:10):
damage control specialists that allow our blood to clot. A Last,
but certainly not least, we've got red blood cells. Their
main purpose is to carry around oxygen from and take
away carbon dioxide to the lungs, where these gases are
inhaled and exhaled, respectively. The protein hemoglobin lets these cells
(01:31):
execute both tasks, a core ingredient in red blood cells,
hemoglobin combined to oxygen and carbon dioxide. Hemoglobin is partly
made up of iron atoms, which give this protein, and
by extension, are red blood cells a crimson color. Since
our platelets and white blood cells are vastly outnumbered by
(01:52):
red blood cells, human blood as a whole looks red,
but like many things, blood exists on a spectrum due
to the pressures of evolution. We've got everything from blue
blooded invertebrates to green blooded reptiles to fish with transparent
fluids in their veins. Today, let's talk about some of
(02:13):
the curious critters with blood in colors other than red.
First up, New Guineas green blooded skinks. New Guineas home
to multiple lizard species from the skink family that have
line green blood. Consequently, their tongues, muscles, and bones are
all various shades of green. Like humans, reptiles have hemoglobin
(02:36):
rich red blood cells, but such cells do not live forever,
and when they break down in our bodies as well
as the lizards, a green pigmented waste product called biliverdin
is created. Most vertebrates filter this stuff out of their
circulatory systems because excess biliverdin can harm cells, including neurons
(02:56):
and DNA. These lizards have a level of verdin in
their veins that would kill a human. Moreover, the pigment
is so densely concentrated that it overrides the hemoglobin and
makes their blood look green. Herpetologists aren't entirely sure why
these lizards possess this trait, but it's apparently a strong one.
(03:18):
In a study published in twenty eighteen, researchers carried out
a genetic survey of fifty one different skinks in Australia, Asia,
and the Islands between them. They analyzed six of the
green blooded New Guinea species in the process. It turns
out that those biliverden loaded reptiles aren't even closely related
to one another. It seems that each of them is
(03:40):
descended from red blooded ancestors, and they evolved green bloodedness independently.
Such an unusual trait wouldn't have evolved six times over
if it didn't offer some kind of benefit. But again
we're not sure what it is. Predators that eat the
lizards don't get sick afterward, and the skinks are no
better camouflaged than their red blooded cousins. It's possible that
(04:04):
the special blood helped their ancestors kill parasites, but more
research will be needed to confirm or refute this. While
we're waiting on that, let's move on to the crocodile
ice fish, so named for their long toothy snouts. The
sixteen species of crocodile ice fish that have been recognized
all live in the ocean waters around in Arctica. These
(04:27):
extremophiles are built to thriving conditions that would kill most
other vertebrates. They frequent brutally cold areas where the water
temperature can plummet all the way down to twenty eight
degrees fahrenheit or negative two celsius. That's below the point
at which freshwater freezes. In such cold water, red blood
cells turn into a liability. That's because blood with the
(04:50):
high percentage of these cells becomes dangerously thick and hard
to circulate when the temperature gets too low. A fish
that thrive in cold waters tend to have proportionately fewer
red blood cells than their warm water counterparts do. But
crocodile ice fish take this to the extreme. Unlike every
(05:10):
other known type of vertebrate animal, they don't have any
red blood cells or hemoglobin at all. Now you might
be thinking, wait a second. Without hemoglobin or red blood cells,
how do the fish circulate oxygen through their bodies. To
get the job done? They enlist the ocean itself. Cold
(05:30):
water is naturally richer in usable oxygen than warm water.
Crocodile ice fish absorbs above this oxygen directly from the
ocean around them and send it into their blood streams.
The blood itself is a colorless liquid, a fact that
really surprised the biologists who discovered these fish in nineteen
twenty eight. It turns out that this cold water oxygen
(05:52):
is so abundant that, upon absorption, it doesn't need to
hitch a ride on red blood cells to get around. Instead,
it can travel from point A to point B inside
the fish's plasma hemoglobin free. But okay, As so far
we've been talking about vertebrate animals, which nearly all use
hemoglobin to circulate oxygen. Many invertebrates use an alternative protein,
(06:16):
hemocyanin both are capable of binding to and transporting oxygen.
But whereas hemoglobin contains iron atoms, hemocyanin incorporates copper. As
a result, blood containing hemocyanin looks markedly different from our
human blood. When hemocyanin rich blood becomes oxygenated, the copper
(06:37):
in it turns it blue. The list of invertebrates that
rely on hemocyanin instead of hemoglobin is a long one,
including crustaceans, spiders, and scorpions. The roster also includes certain mollusks,
like everyone's favorite multi armed brainiacs, octopuses. Yes, octopuses have
literally blue blood and three hearts with which to pump
(07:01):
it in oxygen poor deep sea environments, hemicyanin is better
than hemoglobin, carrying that precious oxygen through in animal's veins.
Octopuses use the protein to stay alive in some seriously
deep waters and at a wild range of temperatures, from
what would be below freezing in fresh water to superheated
(07:21):
near thermal vents. Additionally, hemicyanin helps these tentacled critters regulate
the salt content of their blood so that it matches
that of the water that they're swimming. In next up brachiopods.
These are ocean dwelling animals that resemble clams, though they
evolved independently. Braccupods grow a pair of shells around the
(07:44):
upper and lower surfaces of their squishy bodies, connected with
a hinge at one end, a found in an assortment
of marine habitats. The creatures filter tiny food particles out
of the water. Although there are over three hundred living species,
most people is so brachiopods with prehistoric times because these
hard shelled creatures are disproportionately well represented in the fossil record.
(08:08):
Extant brachiopods do not rely on either hemoglobin or hemocyanin
to ferry oxygen in the blood. Instead, they have heemerthrine,
yet another pigmented protein. Like hemoglobin, it contains iron atoms,
albeit in a different arrangement. Heemerythrine makes deoxygenated blood look colorless,
(08:29):
too faintly yellow. Once the blood starts taking on oxygen,
it adopts a violet, pinkish hue. You'll also see this
kind of blood in marine worms in the class Sypuncula.
They're nicknamed peanut worms because some of them have bodies
that grow in small pointed ovals, looking a bit like
shelled peanuts. These buddies often reside in shallow waters, burrowing
(08:54):
in sand or mud, or taking up in crevices or
unoccupied shells. Other ocean going worms have a different circulatory setup.
If a diver were to spot a live polyket cruising
through the waves, they might mistake it for a sentient
feather duster. Most of these worms are covered in bristles
(09:15):
and tentacles, whose function varies from species to species. Some
have red blood, but others harbor green blood. The latter
use the oxygen binding protein chlorocrurine in place of hemoglobin.
It also uses iron to bind to oxygen, but in
yet another formation, it's what's called dichroic, or too colored,
(09:39):
which means that it can appear to be different colors
in different circumstances. When chlorocrurine is concentrated, its molecules stack
to appear deep red brown, but when it's dilute it
appears green, which means that even if Kermit was right,
and it's not easy being green, at least those new
(10:00):
guinea skinks have some creepy Crawley Company. Today's episode is
based on the article Five Animals whose Blood Isn't read
on HowStuffWorks dot Com, written by Mark Mancini. Brain Stuff
is production of iHeartRadio in partnership with HowStuffWorks dot Com
and is produced by Tyler Klang. Four more podcasts my
(10:22):
heart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever
you listen to your favorite shows.
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