The enterobius is also known as pin worm. It occurs in caecum, colon etc. and is common in children. The females move to the anus of host and lay eggs. The patient scratches these areas and they are transported into the mouth. They have couple of expansions at the anterior end. Their mouth has three lips. They show sexual dimorphism. The female is longer and straight while the male is short and curved. The females have separate anus and genital aperture and these openings are combined in the males. It causes enterobiasis which leads to the itching of anus, inflammation of the colon, nausea, abdominal pain and diarrhoea. They have no intermediate host and are known as monogenetic.