A microscopic filariform (L3) larva penetrates bare skin that touches Strongyloides stercoralis infested soil. It enters the bloodstream ending up in the pulmonary capillaries. There it exits the blood and enters the lung alveoli. It is taken out of the lungs by the movement of microvilli through the bronchus and trachea to the throat where it is swallowed. Eventually it reaches the small intestine where it develops into an adult female by molting twice. The female lives burrowed into the intestinal wall. It reproduces asexually (by parthenogenesis) and releases eggs from which first stage larvae called rhabditiform hatch. They either exit the body in the stool or molt twice into infective filariform larvae. A filariform larva either penetrates the intestinal wall (internal autoinfection) or if already in the anus, it penetrates the outside/perianal skin (external autoinfection). Then it goes through the same routine: blood, lungs, stomach and back to the small intestine where it matures into adult.