Photo Credit: http://cal.nbc.upenn.edu/merial/trems/fascio_a.htm

The adult Fasciola hepatica worms live in the bile ducts of their host's liver. Mature adults begin to produce eggs 2-4 months after initial infection. Eggs laid by adult flukes pass down the bile ducts through the gastrointestinal tract and are released in the host's feces. If the relatively fragile eggs come into contact with water of the appropriate temperature, above 10 C, they will hatch, releasing miracidiae (A) within two weeks. The newly hatched miracidiae must find a suitable Lymanaea snail host within 24 hours of hatching or they will die. When they identify a host, the miracidiae burrow into the snail and begin their next stage of development.

Once inside the Lymanaea, the miracidium loses its cilia and develops into a sac of germinating cells called a sporocyst (B). Each of these germinal cells develops into a redia(C) which then burst through the sporocyst and migrate in the hepato-pancreas of the snail.

The rediae then develop into cercariae (D) which are released out of the snail and swim through the water using their new tails. The cercariae then attach to plant matter in the water and encyst, forming metacercariae (E), the infective form of the fluke.

When a mammalian host consumes the vegetation on which the metacercariae are encysted, the metacercariae excyst in the small intestine (F), burrow through the intestinal wall, migrate across the peritoneal cavity, and enter the liver parenchyma (G). The immature flukes migrate through the liver parenchyma for 6 to 8 weeks, giving rise to the symptoms of acute infection. When they mature, they enter and settle in the bile ducts where after roughly a month they begin to produce their own eggs and the cycle is completed.