Silver nanoparticles 'Ag NPs' appear to be a good choice to manage insect pests owing to their unique features. In addition, green-synthesized silver nanoparticles utilizing plant extracts have vital uses in the area of biology notably in pest control owing to their safety. This paper aims to explore the larvicidal activity of 'AgNPs' generated by the green chemistry procedure from Nerium oleander leaf extract and analyzed their effects on haemolymph proteins of Lucilia sericata. Phytochemical research was undertaken to identify the phytochemicals responsible for reduction and capping of green produced 'AgNPs'. Silver nanoparticles were effectively manufactured utilizing N. oleander leaf extract and silver nitrate, the aqueous plant extract function as a reducing as well as a stabilizing agent of 'AgNPs'. The produced 'AgNPs' were studied by UV–Vis spectra, Transmission Electron Microscope (TEM), Fourier Transforms Infra-Red (FT-IR) spectroscopy and X-ray diffraction (XRD) (XRD). Third instar larvae of L. sericata subjected to varied doses of N. oleander leaf extract and green-synthesized silver nanoparticles. GC–MS study indicated that crude leaf extract include 17 chemicals belong to the phytochemical classes; phenol, Sesquiterpen, sterol, ester, and heterocyclic compounds. UV–Vis spectra indicated a surface resonance peak at 430 nm corresponding to the production of 'AgNPs' and FTIR spectra demonstrated that the synthesized 'AgNPs' are capped with biomolecules which are responsible for reduction of silver ions. 'AgNPs' are spherical in form, the particle size varied from 4 to 32 nm and the average crystalline size was 27 nm. 100 percent mortality was reported in N. oleander-AgNPs treated larvae at 50 ppm (LC₅₀ = 21 ppm) while crude extract exhibited 80 percent mortality at 500 ppm (LC₅₀ = 389 ppm). Also, the examined substances substantially (p < 0.05) lowered the overall protein contents of treated larvae and generated differences in the number of heamolymph protein bands with varied molecular weights as compared to control. The effectiveness in killing L. sericata larvae and stability of N. oleander-AgNPs has made this product a suitable candidate for the creation of a new biopesticide.