The fall armyworm, Spodoptera frugiperda (J. E. Smith), a newly invasive pest, has natural insect enemies that hold promise as biological control agents. Here we analyzed predation rates between natural enemy insect, the syrphid Episyrphus balteatus (De Geer) and S. frugiperda in all paired combinations of all immature stages for each insect in petri dishes. The 2nd and 3rd instars E. balteatus larvae consumed 1st and 2nd instars S. frugiperda larvae, and 3rd and higher larval instars of S. frugiperda preyed on all instar larvae of E. balteatus. The 2nd and 3rd instars larvae of E. balteatus preyed on 1st and 2nd larval instars of S. frugiperda, consistent with the Holling type III response in petri dishes, with a theoretical maximum predation of 77 and 71 individuals in 24 h. The 5th and 6th instars S. frugiperda larvae consumed E. balteatus larvae, also with the Holling type III response, with a theoretical maximum predation on 1st instar E. balteatus larvae were 29 and 36 individuals, respectively. In a plant cage trial study, predation results were similar to those in petri dishes but with a lower predation number. None of the S. frugiperda larvae that fed on E. balteatus larvae developed to adulthood, and only about 20% of E. balteatus larvae that fed on S. frugiperda larvae became adults which had a significantly shorter lifespan than those who consume aphids. This two-way predation study revealed the complexity of S. frugiperda invasion and provided new insights into relationship between pests and natural enemies.