The black widow spider’s circulatory system is considered to be an open circulatory system, in which blood flows freely throughout the body to provide oxygen to organs and tissues while carbon dioxide is being dispersed. However, the heart is constantly beating and pumping blood into the sinuses surrounding the organs of the spider. With this, nutrients are diffused into the cells and the waste materials produced are diffused back into the blood, in which excretion removes the wastes from the body. The main chemical that provides oxygen to the vital organs is known as hemocyanin, which is similar to human hemoglobin. Although not as efficient as hemoglobin, hemocyanin carries oxygen well enough for spiders.