Ray-Bans for Shrimps

Shrimps use the chemical equivalent of Ray-Bans to filter light of different colours into different parts of their eyes.

Rather than evolve separate cones to see separate colours, which is how humans do it, Michael Bok and his colleagues at the University of Maryland have discovered that mantis shrimps instead have a single population of light-sensing cells. But different cells across the eye are coated with a "filter" chemical that screens out different wavelengths or colours of light so that the cell beneath will only respond when a specific colour shines upon it.

The chemicals that do this are called mycosporine-like amino acid (MAA) pigments, which the researchers speculate the shrimps obtain through their diets. These chemicals are known as natural sunscreens because they block out UV, and their use in the shrimp's visual system means that this animal is unique in being able to see and distinguish at least five different colours of UV light.

As other members of the animal kingdom cannot see light of these wavelengths, this, the researchers tantalisingly speculate, might endow these shrimps with a covert means of communication that other species are oblivious to. It also means that these quick-striking predators may be able to see beyond the camouflage adopted by their prey, which is likely to tailored to work best in visible light rather than UV.