Ascaris adults are parasitic in the small intestine of human beings or other animals, mostly in the jejunum, and feed on semi-digested food. After mating between male and female adults, female insects lay eggs, and the eggs are discharged with feces, which pollutes the environment. The fertilized eggs are cool, moist and rich in oxygen, which is suitable for ascaris lumbricoides fertilized eggs.

At the appropriate temperature (2 1~30℃), the eggs in the eggs developed into the first stage larvae after two weeks, and developed into infected eggs after molting for the first time one week later. During the infection period, eggs are swallowed and larvae hatch in the small intestine. Larvae can secrete hyaluronidase and protease, invade intestinal mucosa and submucosa, drill into small veins or lymphatic vessels of intestinal wall, enter the liver through veins, then go through the right heart to the lungs, break through capillaries and enter the alveoli, where they molt for the second and third time, then move to the pharynx along the bronchus and trachea, be swallowed by the host, and molt for the fourth time in the small intestine through the esophagus and stomach. It takes about 2 months from the time when infected eggs enter the human body to the time when females begin to lay eggs, and the life span of adults is about 1 year.