Nikos Gavalas and Alexandra Tricha, both 31 and trained as agriculturalists, were frustrated working on poorly paying, short-term contracts in Athens, where jobs are scarce and the cost of living is high. So last year, they decided to start a new project: growing edible snails for export. As Greece’s blighted economy plunges further into the abyss, the couple are joining with an exodus of Greeks who are fleeing to the countryside and looking to the nation’s rich rural past as a guide to the future. They acknowledge that it is a peculiar undertaking, with more manual labor than they, as...