Similar to other complex organisms, the red earthworm has a closed circulatory system, meaning that its blood is constantly being circulated throughout the worms body with the help of blood vessels. Despite the fact that the red earthworms doesn't possess lungs or gills to obtain oxygen with, oxygen manages to get into the worm by diffusing through the outside layer of the worm. Once oxygen makes its way into the worm, its dorsal blood vessel sends it to the five hearts the red earthworm possesses near its esophagus, who then siphon it into the lower, ventral blood vessel. The ventral blood vessel is in charge of pumping oxygen rich blood to all the segments and organs of the worm that require oxygen. Each segment of the worm is in possession of a small blood vessel that pumps blood from the ventral blood vessel back into the dorsal blood vessel, bringing the cycle back to where it started. An earthworm is most comfortable in moderately moist soil, as it can retrieve the oxygen it needs from the moist soil. The red earthworm will die if the soil it is living in is too dry or wet, or it will surface in order to get oxygen directly from the atmosphere.