3d illustration of a the nematode worm Strongyloides stercoralis. This worm is unusual because it has both free-living and parasitic life cycles. In the parasitic life cycle, larvae infect the human host by skin penetration. The larvae travel to the lungs, where they are coughed up and swallowed, thus moving to the intestines where they mature into female worms. These females can produce larvae parthenogenetically, which pass out of the host in faeces. The larvae can then either penetrate the skin around the anus to begin a new infection or they can complete their development in soil to become free-living worms.