A cercaria, larva of the liver fluke (Fasciola hepatica), a parasitic flatworm. Cercariae are free-living larvae which emerge from the liver fluke's intermediate host, certain species of freshwater snail. The larvae form cysts on nearby vegetation, which are ingested by ruminants, or sometimes by humans. Immature flukes emerge from the cysts and migrate into the bile ducts where they mature and pass eggs into the host's faeces. The eggs can contaminate water and hatch into larvae which infect snails, thus continuing the fluke's life cycle. Liver flukes cause fascioliasis, a liver disease with symptoms including digestive problems, fever, pain, anaemia and jaundice. Footage filmed at Ridgeway Research, Gloucestershire, United Kingdom.