Study of the role of the binocular vision in mantids to estimate long distances, using the deimatic reaction as experimental situation

Abstract

1. Deimatic reactions (DR's) of the mantid Stagmatoptera biocellata were elicited by birds (shiny cow-birds and Java sparrows) placed at six different distances. A special set-up was used for successive presentations (Fig. 2). The relationship between the bird-mantid distance, on the one hand, and the occurrence and strength of the DR, on the other hand, was demonstrated (Fig. 3). Normal mantids faced with shiny cow-birds presented a distance-DR's curve similar to that of the normal mantids faced with Java sparrows. Monocular mantids, i.e. mantids whose left eyes were blinded, presented very different distance-DR's curves according to the species of bird they faced (Fig. 3). A graphic method (Figs. 4, 5) revealed that monocular mantids faced with Java sparrows at the shortest distance performed the same as those faced with shiny cow-birds at 30 cm; with Java sparrows at 15 cm as with shiny cow-birds at 45 cm; and so on. A method was designed to determine the absolute size of the image casted by both birds at the six different distances (Fig. 10). A clear-cut correspondence was found between distances at which a similar performance was evoked and distances at which images of similar size were projected. The conclusion was that a mantid deprived of its binocular vision can recognize shapes (i.e. predators) and respond with a DR, but it reacts only in accordance with the absolute size of the image, i.e. without distance estimation. 2. Results showed a response decrement with trials (Figs. 8–10) suggesting that an habituation process is involved.