Insects do not have lungs, instead, they breathe through a series of tiny tubes called tracheae. However, the one organ that insects do not have is a true heart. Instead, they have a long tube-like structure called the dorsal vessel, which pumps hemolymph (a fluid similar to blood) throughout their bodies. The dorsal vessel is aided by openings called ostia that allow the hemolymph to flow back into the vessel.