The larva and pupa of Amyna axis (Guenee, 1852) are described and illustrated, and observations are provided on the insect’s life history and larval biology. Larval, adult, and life history characters support the transfer of Amyna Guenee from Acontiinae Guenee, 1841 to Bagisarinae Crumb, 1956. The phylogenetic placement of the Bagisarinae is enigmatic; some adult and larval features indicate that the subfamily is a basal trifid proximate to Acontiinae, whereas other larval and life history characters suggest an association with Scoliopteryginae, a basal quadrifid group. Larvae exhibit a green-to-black color polyphenism presumably linked to larval density, with darker phenotypes occurring during outbreak densities. Parallel color shifts that occur in other Lepidoptera are briefly discussed.