The present study set out to compare two predictive models,Holling (1966)andHardman and Turnbull (1980), to described the arousal space for the aquatic sit-and-wait predator, Ranatra dispar. When tested in the horizontal plane the fit of Holling's model was good, although a better fit was achieved by using the untransformed "angle of prey to body axis" term θ. The second, multiple regression model, gave smaller residuals for low food deprivation periods but larger for longer periods. In the vertical plane the Holling model was unsatisfactory. It is suggested that the changes in number and size of ommatidia from dorsal to ventral region of the eye is largely responsible. A multiple regression model is described that predicts the arousal field of R. dispar in the vertical plane. It is suggested that the general applicability of such models to other visual predators is restricted if apparent hunger effects are not included in their development.