Crabs and Their Visual World

The visual systems of semi-terrestrial crabs are exquisitely tuned to the visual properties of the environments they inhabit and to the visual tasks they face. We review here the inventory of these visual tasks in the context of orientation, navigation, predator avoidance, foraging, territorial interactions, and communication. In some cases, specific visual processing demands are reflected in detailed specializations of compound eyes, and also in the organization of behavior. Because many crabs are central place foragers with a limited action space, they are superb subjects for analyzing image processing demands and neural mechanisms under natural conditions, a prerequisite for understanding the evolution of visual systems. Studying vision in crabs shows that visual information is not distributed uniformly in the visual field, that vision is context-dependent and pragmatic, and that there are perceptual limits to what animals can know.