Science Fact Finder | The Animal World - Do All Animals Have Red Blood?

Do all animals have red blood?

Not all animals have red blood. The color of blood depends upon the type of compound or respiratory pigment within the blood that transports oxygen from the lungs to the tissues. In all vertebrates (animals having a backbone) and a few invertebrates (animals lacking a backbone), an iron-containing protein called hemoglobin is responsible for oxygen transport. Hemoglobin is a red pigment and gives the blood a red color.

Annelids (segmented worms) have either a green pigment, chlorocruorin, or a red pigment, hemerythrin. Some crustaceans (invertebrates with jointed bodies, such as crabs and shrimps) have a blue pigment, hemocyanin, in their blood. Cockroaches have no respiratory pigment, thus their blood is colorless.

Source: New Encyclopaedia Britannica, 15th ed., vol. 2, p. 290.

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