Do Spiders Have Blood?

Spiders do not have blood in the same way that humans and other vertebrates do; instead, they have a fluid called hemolymph that performs the same function. Hemolymph is distinguished from blood in its composition and variety of uses as compared to blood.

Blood in humans and other animals with backbones is composed of a fluid called plasma and the variety of cells that float through the plasma. In humans, red blood cells carry oxygen, white blood cells fight infections and platelets close wounds by forming scabs. In fish, only red and white blood cells are present, but they do similar jobs.

Creatures such as spiders do not have red or white blood cells or platelets circulating through their hemolymph. Their hemolymph contains dissolved sugars and proteins, bringing food to cells, as well as hormones to regulate bodily functions and a pigment called hemocyanin that transports oxygen to cells. Rather than white blood cells, spiders have hemocytes that function as an immune system.