Alaria adult attached to the small intestine mucosa. Photo and illustration adapted from Bowman, D.D., Georgis' Parasitology for Vetrerinarians , sixth edition, 1995. Page 126 - 127.
Eggs leave the cat in the feces and hatch in fresh water.
The miracidium enter snails of the genus Helisoma and develop to sporocysts, daughter sporocysts and finally to cercariae. The cercariae leave the snail and penetrate the skin of a leopard frog tadpole where they develop into mesocercariae. If a frog, snake, bird, or any mammal, other than the raccoon or cat, eats the infected tadpole, the mesocercaria invade the tissues of this paratenic host and remains as a mesocercaria. If a cat eats an infected tadpole or paratenic host the mesocercariae will penetrate into the body cavity and migrate through the diaphragm to the lungs where some of them develop into metacercariae. The metacercaria is carried up the trachea and is swallowed.