Visually mediated snapping in the bulldog ant: A perceptual ambiguity between size and distance

Abstract

1. The isolated head of the bulldog ant,Myrmecia gulosa, snaps its mandibles in a predictable way in response to an approaching target, allowing the isolation of a single visually mediated component from the complex prey capture repertoire of intact animals. 2. The timing of the response depends on both the size of the target and its position relative to the animal's visual midline (Figs. 2, 12, 13). Except for a latency component, the snapping is velocity independent (Fig. 3). 3. Only 14% of the animals tested continued to respond to the targets when vision in one eye was occluded. Although monocular responses occurred at the same mean target distance as binocular responses, the variance was significantly greater (Figs. 4, 5). 4. Optical measurements of the visual field ofM.gulosa indicate a binocular overlap of nearly 60° (Figs. 7, 9). 5. Correlation of behavioral and optical measurements suggest that the snapping is triggered when the edge of any size target comes into the visual field of a small group of facets (Figs. 9, 10). 6. These experiments with the isolated head preparation show that the bulldog ant cannot judge the absolute distance of a target in the visual field when limited to primary visual cues, and suggest that two eyes are better than one simply because they provide more input.