Spatial vision in the praying mantis: is distance implicated in size detection?

Summary The catching behaviour of the praying mantis Sphodromantis viridis is investigated in order to see whether or not the detection of prey size depends on the detection of prey distance. A first experiment demonstrates the mantid's ability to discriminate small differences in prey distance. Next, the preferred prey size is determined for a number of distances with the preference being indicated by the strike rates. The results demonstrate that the mantid's judgements of size are based on a relative (angular) scale rather than on an absolute (millimetre) scale. This is a strong piece of evidence that a relation between size and distance does not exist. Finally, the attack behaviour is analysed in detail, but it turns out that prey size has no effect on the organization of both the lunge of the body and the strike of the raptorial forelegs. Taken together, the findings of this study suggest that mantids localize prey with precision, but they do so without any knowledge of the absolute size of prey.