Ascaris: The intestinal roundworm, a worm that lives in the small intestine.

Infection with ascaris is the most common worm infection in humans. It is termed ascariasis.

Ascaris eggs are found in the soil. Infection occurs when a person accidently ingests (swallows) infective ascaris eggs. Once in the stomach, larvae (immature worms) hatch from the eggs. The larvae are carried through the lungs then to the throat where they are then swallowed. Once swallowed, they reach the intestines and develop into adult worms. Adult female worms can grow over 12 inches (4.8 cm) in length. Adult male worms are smaller. Adult female worms lay eggs that are then passed in feces; this cycle takes between 2 and 3 months. Adult worms can live 1 to 2 years.