Abstract

Imagine life without colour. Many of the rich layers of information in our visual world would disappear and simple tasks, such as finding a red apple in a tree, would be far more difficult. There are many examples of animals in nature that do not have colour vision, yet some have managed to develop high-performance eyes that, in some respects, far surpass our own visual capabilities. One of the ways that animals have achieved this is to make use of the polarization of light, rather than colour.

Scientists have been interested in how animals see and use the polarization of light ever since the early studies of Karl von Frisch in the 1940s, which demonstrated that bees can use the polarized sky pattern to navigate. Almost all work since then has focussed on understanding the intricacies of polarized light navigation using non-imaging parts of the eye. Recently, it has become clear that some animals, such as fiddler crabs, mantis shrimps, and cuttlefish, have high-performance polarization vision across the image-forming parts of the eye, which they use to detect objects and, in some cases, hidden communication signals. This is comparable to the discovery that some animals can see ultraviolet colours beyond our own human visual spectrum, thus opening up a new layer of information in their visual world.