The coral bean, Erythrina herbacea, is reported as a new host for Automeris io in north-central Florida, based on a single batch of larvae found on this plant in nature and reared through on it in the laboratory. However, the consequent laboratory rearing showed a high cost associated with using this host plant. The mortality of young larvae of the F-2 generation reared on E. herbacea was very high (over 90%), and much higher than that of control larvae, which were reared on mature leaves of Quercus nigra (14–38%). The leaves of E. herbacea, known for their toxic alkaloids, were extracted with methanol, made into a water solution, applied on the mature leaves of Q. nigra, and fed to 1st instars of A. io. This produced no negative effect on the caterpillars. While the mature leaves of Q. nigra produced low mortality in young caterpillars, the young terminal leaves of this plant were as lethal to A. io as leaves of E. herbacea. Additionally, it was noted that rearing larvae on E. herbacea (a diet with a higher N2 content) led to faster larval development and smaller adult moths. The A. io larvae in this study developed during 63–100 days and underwent seven larval instars, which contradicts many popular accounts of the fifth instar being the final in A. io. Finally, Prunus angustifolia proved to be an unsuitable hostplant for A. io, as feeding on this species led to the arrested development of larvae and their eventual death.