Why is Spiders Blood Blue?
WouterWhen you hear about spiders’ blood, you may be confused. You may wonder why is their blood blue? Or you might be surprised that octopuses, shrimp, crayfish, mussels, scallops, crabs, and lobsters all have blue blood.
Blood is designed to carry oxygen throughout the body. It is also used to transport nutrients and hormones. The human body’s blood contains the haemoglobin molecule, which binds oxygen with iron atoms.
The oxyhaemoglobin molecule reflects red light, while the haemocyanin molecule reflects blue light. When these two molecules interact, they reflect blue light, giving the blood its blue colour.
Although spiders have blue blood, their blood is not a bright blue. This is because of the haemocyanin molecule, which is copper based.
The copper atom is in the middle of the hemocyanin protein. When oxygen is present, the hemocyanin molecule becomes blue. However, when the haemocyanin protein is not carrying oxygen, it appears as clear as water. The hemocyanin molecule absorbs all colors except blue.
Spiders’ blood is also different from other animals’. While other animals’ blood has red cells, spiders do not.
Most modern spiders have one pair of book lungs. The book lungs are hollow leaf-like structures that are located below the abdomen. They are connected to a tube.
Other than hemocyanin, spiders’ blood is not colored. However, it does have other fluorescing compounds that can help it serve a local purpose. For example, it is often used to raise blood pressure during moulting.
