Why is Blood Red?

What is it in our blood that makes it red, and why are other animals different? Biology - Human Body - Learning Points. Haemoglobin is the most efficient oxygen carrier and provides the red pigment in blood. Not all animals have red blood. The horseshoe crab has blue blood because its oxygen carrier, haemocyanin, contains copper. Deep sea worms' oxygen-carrying molecule is hemerythrin, which has a pink pigment. A Twig Context Film. Reinforce and extend the learning required by the curriculum. Twig’s context films show abstract concepts in action in the real world.