An earthworm has a total of five hearts. These hearts are very simple as is an earthworm's circulatory system and do not complete the complex jobs that a human heart does. The main function of an earthworm's five hearts is to pump blood through the body.

Worms do not have lungs or brains, using a reactive central nervous system to move through dirt and react to touch. Without lungs, there is no carrying of oxygen from the lungs to the hearts. Instead, an earthworm breathes through its skin. An earthworm must remain moist in order to live. If it dries out it will die and if it remains submerged under water for an extended period of time it will suffocate.