Abstract Phytochemical similarities among ancient Angiosperms presumably played a role in the ecological and evolutionary diversification of the swallowtail butterflies (Papilionidae). Host family feeding specialisation is typical of most Papilionidae species, but field records of oviposition are rare for most swallowtail butterflies. It is even more uncommon to witness oviposition and larval feeding on new host plant species, especially in plant families not previously reported for the butterfly species. Oviposition by a female on a new host, or even on a toxic plant, may represent ancestral behaviour (with a loss of larval acceptance, detoxification or processing abilities) or novel behaviour (providing genetic variation for a potential expansion of host range, or host shift). We document the oviposition, larval use and pupation of the Annonaceae specialised and geographically widespread Graphium eurypylus on a Magnoliaceae species, all under field conditions in Queensland, Australia. This is the first time such field observations of oviposition and larval feeding on Michelia champaca (Magnoliaceae) have been documented anywhere for this species.