Abstract: Background and Objectives: Tetranychus urticae is a pest but also a resource of bio-nanoparticles which could be used as an effective biocide. The aim of this study was to biosynthesize silver nanoparticles (AgNPs) by Tetranychus urticae against Spodoptera littoralis. Materials and Methods: Biosynthesized silver nanoparticles (AgNPs) which coated by biogenic amines resulted from exploded mite’s bodies were able to control the cotton leafworm, Spodoptera littoralis under laboratory conditions. Results: Bio AgNPs caused mortality with 91.24 and 83.77% in case of treated 2nd and 4th larval instars in comparison with control 10.39 and 7.02%, for the same previous arrangement. While, malformation was appeared clearly in the metamorphosis stage to pupal stage after alive treated larvae. Subsequently, oxidative stress was increased and indicating that reactive oxygen scavengers were reduced drastically in interaction effectively with induced treatments. Conclusion: Current research is a novel trend to control pest by another pest which could present bio AgNPs as a biocide and also cause malformation.