The tapeworm is one of the most common parasites in the world. It is estimated that one-third of the world's population is infected with tapeworms. The worm is also found in pets and wildlife, and it is one of the most common causes of human disease. The tapeworm has a complex life cycle. After ingestion, the tapeworm attaches to the wall of the small intestine and begins to grow. The worm will then migrate through the intestines, causing a host of symptoms. It is not unusual for a tapeworm to cause diarrhea, cramps, and abdominal pain.