Adults and larvae in the subfamily Arctiinae (family Erebidae), along with their host plants and the parasitic wasps and flies that attack them, are important components of most terrestrial food webs, but basic taxonomic and life-history knowledge for the arctiines of the Neotropics is still poorly known. This is true for most groups of Lepidoptera in hyperdiverse countries such as Ecuador. To examine host affiliations and natural enemies in diverse ecosystems, we collected 6,243 arctiine caterpillars (representing 821 larval morphospecies) at elevations ranging from 400 to 3,500 m as part of a larger ecological and taxonomic survey of trophic associations centered at the Yanayacu Biological Station in Napo province, eastern Ecuador. Here, we provide a brief review of the systematics of Neotropical Arctiinae, provide basic information on host affiliations and parasitism rates of arctiines reared from Napo province in Ecuador and describe the immature stages of 16 species encountered in the region.