Do spiders have blood?
Yes. Spiders have an open, blood circulatory system. This sort of blood system has a heart, arteries and veins but no capillaries. The heart is tubular with a single cavity and with valves to maintain the flow of blood always in the same direction. The spider’s blood is pale blue due to the presence of haemocyanin dissolved in the lymph. There are some blood cells but they are for wound-healing and defense against infection. There are no special blood cells like the human red cells which carry oxygen around the body.
