When we think of blood, we automatically picture a bright red fluid. However, the animal kingdom holds some fascinating exceptions to this rule.
Several creatures have evolved with blood in surprising colors like blue, green, and purple. These unusual hues aren’t just for show; they result from different oxygen-carrying molecules that help these animals thrive in their specific environments.
This list is for general information only. Blood colour varies by species and environment, and these examples are based on information gathered from scientific sources.
1. Leech (Certain Species)
Not all leeches have red blood. Some species use a rare pigment called chlorocruorin, which gives their blood a greenish tint. Unlike the iron-based haemoglobin found in most animals, chlorocruorin works well in the low-oxygen waters these leeches inhabit.
While it carries oxygen less efficiently than haemoglobin, it’s perfectly adapted to their environment. This surprising twist shows how even small, overlooked creatures have evolved unique ways to survive.
2. Horseshoe Crabs
Ancient mariners of the ocean floor, horseshoe crabs have survived relatively unchanged for over 450 million years. Their striking blue blood contains copper-based hemocyanin instead of the iron-based hemoglobin found in humans.
This remarkable blue blood has become invaluable to medical science. Scientists use it to test for bacterial contamination in vaccines and medical implants because it coagulates around harmful bacteria. A single quart can be worth thousands of dollars, making these prehistoric creatures literally worth their weight in gold.
3. Octopuses
Masters of disguise with problem-solving abilities, octopuses possess three hearts and blue blood. The copper in their hemocyanin oxygen-carrier creates this striking azure hue, perfectly adapted for deep, cold waters where oxygen is scarce.
Unlike our red blood cells that constantly circulate, octopus blood is less efficient in warmer waters. This limitation explains why these brilliant cephalopods prefer cooler depths. Their remarkable circulatory system pumps this blue fluid through their body, supplying oxygen to their large brains and enabling their famous intelligence.
4. Squids
Rocket-like propulsion systems of the sea, squids zoom through ocean depths with copper-rich blue blood coursing through their streamlined bodies. Their hemocyanin works brilliantly in the cold, oxygen-poor environments they call home.
Unlike mammals, squids have developed this alternative oxygen-transport system that turns their blood a vivid blue when oxygenated. Some deep-sea species have evolved additional adaptations, with blood that works efficiently under the crushing pressure of the ocean depths. Their remarkable circulatory system supports their high-speed hunting lifestyle.
5. Lobsters
Beneath their red shells (which only appear after cooking), lobsters harbor a surprising secret—blue blood flowing through their veins. This cerulean fluid contains copper-based hemocyanin that efficiently binds oxygen in cold marine environments.
The blue coloration becomes particularly visible in their uncooked state. When examining a live lobster’s underside, you might glimpse this unusual hue through thinner sections of their exoskeleton. Their evolutionary adaptation to cold waters explains this copper-based blood system, which functions better than iron-based blood in low-temperature conditions.
6. Sea Cucumbers
Resembling their vegetable namesakes, sea cucumbers are marine animals with a surprising feature—violet blood containing the protein hemerythrin. These echinoderms use this unique oxygen carrier instead of the more common hemoglobin found in vertebrates.
When threatened, some species perform an astonishing defensive maneuver, ejecting their internal organs through their rear end! This sticky mass distracts predators while the sea cucumber escapes. Their purple blood supports their slow metabolism, perfectly suited to their unhurried lifestyle of sifting through ocean sediments for food particles.
