Observations of fall army worm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), larvae infesting plots of Miscanthus × giganteus Greef and Deuter ex Hodkinson and Renvoize prompted laboratory-based tests of survival, development, and feeding preferences on leaf tissue from M. × giganteus and switchgrass, Panicum virgatum L. Survival from hatch to pupation was >70 and 50% for fall army worms reared on switchgrass and M. × giganteus, respectively, although survival of the S. frugiperda rice strain was significantly greater than the corn strain on both crops. Developmental times from hatch to pupation or adult emergence showed effects of crop and S. frugiperda host strain, but analysis of an interaction revealed developmental times for the rice strain were similar on both crops, whereas corn strain larvae showed delayed development on M. × giganteus relative to switchgrass. Analysis of larval (10 d) and pupal masses showed a similar pattern, with effects of crop and an interaction (at 10 d), but only the mass of corn strain larvae feeding on M. × giganteus was reduced relative to the other crop and strain combinations. In choice tests, neonates of both corn and rice strains showed a strong preference for feeding on young tissues rather than mature leaves of M. × giganteus or switchgrass, but they also clearly favored corn, Zea mays L., leaves over either of the perennial grasses. Results indicate both plants are potential hosts for S. frugiperda, but additional information is needed to understand under which scenarios and to what degree fall armyworms may damage perennial grasses grown for biofuel production.