The spotted clover moth, Protoschinia scutosa (Denis & Schiffermüller) (Lepidoptera: Noctuidae), is an important polyphagous pest that is widely distributed in the world. P. scutosa overwinters as pupae in agricultural soils in Northern China. Yet, it is unclear whether P. scutosa also engages in seasonal migration over mid- to long-range distances. In this study, we employ light trapping, field surveys, and ovarian dissection of captured adults over a 2003-2015 time period to assess P. scutosa migration in Northern China. Our work shows that P. scutosa migrates across the Bohai Strait seasonally; the mean duration of its windborne migration period was 121.6 d, and the mean trapping number was 1053.6 moths. Nightly catches of P. scutosa were significantly different between months, but the differences between years were not significant. During 2009-2011 and 2013, the monthly proportion of migrating females (65.5%) was significantly higher than that of males and showed no difference between months. In May to June, the majority of females (May: 63.0%; June: 61.1%) were mated individuals with relatively high level of ovarian development; however, in August and September, most females were unmated. The mean proportion of mated females was significantly different across months but did not differ between years. The results of long-term searchlight trapping and ovarian dissection indicate that P. scutosa exhibits a seasonal characteristic of typical population dynamics and reproductive development of migratory insects. Our work sheds light upon key facets of P. scutosa ecology and facilitates the future development of pest forecasting systems and pest management schemes.