Qualitative and quantitative SPE followed by HPLC-TOF/MS determination of pyridalyl and its potential metabolites in the excrement of Helicoverpa armigera (H. armigera) and Spodoptera exigua (S. exigua) was developed. Two potential metabolites, MP1 and MP2, have been confirmed, and a reported metabolite in mammals, MP3, was indicated to be a product of the hydrolysis of pyridalyl. In addition, the content of pyridalyl, MP1 and MP3 in excrement were similar in both pests, while the content of MP2 was 13% greater compared with its counterpart from S. exigua. This may be due to different metabolic processes in mammals and two Lepidoptera pests. The metabolic pathway of pyridalyl in both pests was then proposed based on the preceding results. Compared with reported isotope-labeled strategies, the proposed method cut down experimental time from several days to 2 hours, and reduced sample consumption from several grams to 30 mg.