An oligochate, Limnodrilus variegatus, and a chironomid, Chironomus riparius, were selected for analyzing response behaviors after the specimens were exposed to an insecticide, Diazinon, at low concentrations (1-10 ppb). The movement tracks of the specimens were individually recorded in 2-dimension in observation chambers before (1 day) and after (1 day) the treatments. While the point data (i.e., location of the specimens) were tracked for the chironomid larvae, the line data (i.e., body shape of the speciemens) were observed for the oligochates. Changes in segment length and angle between the body segments were further used for addressing deformation and abnormal body movements of the oligochate specimens. The parameters featuring the movement tracks of the specimens were selected to quantitatively characterize response behaviors, while artificial neural networks were applied to patterning of the movement tracks before and after the treatments. Decrease in activities and intermittent occurrence of abnormal behaviors were accordingly detected by the networks after the treatments.  The study suggested that computational analysis on response behaviors of benthic macro-invertebrate would be useful for in situ monitoring in ecotoxicological risk assessment in aquatic ecosystems.