After getting in your mouth, the eggs pass through the digestive system. The eggs hatch in the small intestine, and the baby worms grow and move on to the large intestine. There, the pinworms grab onto the wall of the intestine. After a few weeks, the female pinworms move to the end of the large intestine, and they come out of the body at night to lay their eggs around the anus.

The amount of time that passes from when someone swallows the eggs until the worms lay new eggs is about 1 to 2 months.