Insects have an outer bilateral exoskeleton to which the muscles are attached and which provides protection for internal organs. The major systems in insects are the circulatory, respiratory, nervous, muscular, digestive, and reproductive systems. In the circulatory system, blood is pumped by the heart in a tube to the aorta, the head, and to other organs then enters the ostia openings along the sides of the tube back to the heart. An insect's blood, like ours, carries food and waste products to and from the cells of the body. But unlike our blood, it has little to do with bringing oxygen to the cells.
Insect blood is greenish, yellowish, or colorless.
Few insects have red blood. The respiratory systems carries oxygen to cells and takes away carbon dioxide by means of a system of tubes. An insect breathes by means of tiny holes, called spiracles, along the sides of its body. The nervous system consists of a brain receiving information from the eyes and antennae. It controls the insect's body activities as a whole.