Earthworms and Digestion

The prostomium is the mouth of the earthworm. Since it has no jaws or teeth, the earthworm uses its muscular pharynx to suck in soil containing food. The food particles and soil go through a long esophagus into a round organ called a crop. The crop stores the food temporarily. Then it is forced into a very muscular organ called the gizzard. The gizzard contracts and expands, causing grains of sand and food to rub together. In this way, the food is ground up. Food is digested in the intestine, which stretches from segment 19 to the end of the worm. Here enzymes chemically break down the food. Then the digested food is absorbed by the blood circulating through the intestine walls. The earthworm's digestive system can be thought of as a tube within a tube.

The complicated organs of the digestive system take up most of the anterior half of the earthworm's body. The earthworm ingests large amounts of soil, which has organic matter in it. The useless inorganic matter goes through the worm with no change. This is often left on the surface of the ground in the form of castings. As the earthworms feed, they loosen the soil, making it easier for air and water to enter. Their wastes also add to soil fertility. If there were earthworms, the soil could not support crops, grasses, and other plants.