Parasites lost – do invaders miss the boat or drown on arrival?

Host species that colonize new regions often lose parasite species. Using population arrival and establishment data for New Zealands introduced bird species and their ectoparasitic chewing lice species, we test the relative importance of different processes and mechanisms in causing parasite species loss. Few lice failed to arrive in New Zealand with their hosts due to being missed by chance in the sample of hosts from the original population (missing the boat). Rather, most lice were absent because their hosts or the parasite themselves failed to establish populations in their new environment. Given they arrived and their host established, parasite persistence was more strongly related to factors associated with transmission efficiency (number of host individuals introduced, host body size, host sociality and parasite suborder) than parasite propagule pressure and aggregation. Such insights into parasite success are invaluable to both understanding and managing their impact.