The aim of the study was to determine insecticidal potential of three plant extracts (Calatropis procera, Eucalyptus globulus and Mentha arvensis) and crude venom of an orb-web spider, Neoscona theisi, in the laboratory using Musca domestica and Aedes aegypti as model insects. Laboratory bioassays were conducted against three doses of plants extracts (0.2 mg/ml, 0.4 mg/ml and 0.6 mg/ml) and spider venom (10 µg/ml, 20 µg/ml and 30 µg/ml). Ellman et al.'s (1961) method was followed to estimate the activity of acetylcholinesterase of insects. Calatropis procera was found to be more effective in killing the insects. The mortality rate was increased with an increase in plant extract or venom dose. Calatropis procera inhibited acetylcholinesterase more proficiently as compared to the M. arvensis and E. globulus extracts. Crude spider venom also significantly inhibited the estimated activity of acetylcholinesterase in M. domestica and Ae. aegypti. It is concluded from the study that both plant extracts and spider venom inhibited the activity of acetylcholinesterase in M. domestica and Ae. aegypti but C. procera is more efficient in killing the insects.