In 1989, just 26 Partula nodosa snails remained after a failed biological-control effort nearly wiped out the species. The survivors were sent to Detroit Zoo, where conservationists began a successful breeding programme. Decades later, more than 17,000 Partula snails have been reintroduced to their native islands. Hundreds continue making the 5,000-mile journey to Tahiti, helping restore both ecosystems and Polynesian cultural heritage.