Human ascaris (Ascaris lumbricoides hominis) is a human parasite, feeding in the digestive system and in the lungs. It has an oval shape of the body, coloured pale pink. There are four longitudinal lines along the body. The dorsal and abdominal lines are thin and white, and the lateral lines are brown and thicker. Human ascaris is sexually heterogeneous, females are up to 40 cm long, the size of males ranges from 10 to 32 cm. Adult females live in the human small intestine. They lay up to 200,000 eggs a day, which leave the host’s body with the faeces. After a few weeks, the eggs develop into larvae which wait to be ingested by a human. In the intestine, the larvae escape from the egg sheath and enter the blood vessels through the intestinal wall, starting to migrate with blood to the lungs. They reach the pulmonary alveoli, where they moult twice. After reaching approx. 2 mm long they begin to move up the respiratory system: through bronchioles, bronchi, trachea to the larynx, from where, reflexively swallowed, get into the stomach and further into the intestine. They mature here. After approx. 2 months after infection they begin to multiply. The disease caused by human ascaris is called ascariasis and usually manifests itself in overall weakness, dizziness, facial swelling, excessive excitability of the patient and allergic reactions. When the infection is massive, complete intestinal obstruction may occur. Infection by the human ascaris can take place by eating unwashed vegetables that have been fertilized with human faeces, or by drinking contaminated water (e.g. when swimming in a lake, less often in a swimming pool).