The eggs shed by adult flukes are expelled with the feces. Once outside the host, the larvae called miracidia hatch out of the eggs in a few days. These larvae can survive for weeks off a host provided there is enough humidity. They die quickly in a dry environment. Miracidia can swim and penetrate actively into the snails where they develop successively to sporocysts, rediae and cercariae, the usual larval stages of most fluke species.