The immature stages ofAricoris propitia(Stichel) are described and illustrated for the first time, using both light and scanning electron microscopy. Females oviposit in at least seven host-plant families, always in the presence of fire ants (Solenopsis saevissima(Smith) complex), without being attacked by them. Larvae are tended by ants during all larval and pupal stages. From the fourth instar on, larvae feed at night and rest during the day inside underground shelters constructed by ants on the host plant roots, and where pupation occurs. Several observed features, including ant-mediated oviposition, persistent ant attendance throughout all instars, and high spatiotemporal fidelity indicate thatA. propitiais a myrmecophile obligately associated with fire ants. We proposeA. propitiaas an extraordinary model for studies on ant-butterfly evolutionary history in the Neotropics.