Video: Shimmery sea sapphires disappear in a flash

Red and blue and green and violet and… Invisible. Sea sapphires have been described as “the most beautiful animal you’ve never seen”. Even when you do see them, they can vanish in an instant (see video, above). But how do they pull off their trick?

This tiny crustacean has alternating layers of hexagonal guanine crystals and cytoplasm on its back that reflect light in a sparkling array of hues. Different species shimmer in different colours, ranging from gold to blue.

The colour is determined by the distance between the crystals and the angle at which light hits them.


In blue sea sapphires, the distance between the crystals is about the same as the wavelength of blue light, so the animals appear blue.

The angle of light hitting the sea sapphire also affects the colour and lets it perform its disappearing act. For the species in the video, for example, the animal’s tilt of 45 degrees causes the reflected light to slip into the ultraviolet spectrum, and the animal becomes invisible to our eyes.

Only the males have these amazing colours, the females are completely translucent. Males swim in spirals, probably to show off their shimmering hues to potential mates, says Lia Addadi at the Weizmann Institute of Science in Rehovot, Israel.

“An intriguing question that still remains is whether the differences in colour are genetic and each male is born with a defined colour, or whether they can control the reflected colour,” says Addadi.

Understanding how the light reflection trick works could inspire new reflective or anti-reflective coatings in glasses, mirrors and optical display systems, says Addadi.

Journal reference: Journal of the American Chemical Society, DOI: 10.1021/jacs.5b05289