Blue is a very rare color among animals. Only a handful of the Earth's creatures sport blue in their coloration. Why is it so rare?
In 12 elusively blue animals, MNN's Catie Leary explains, "While plants can produce blue pigments thanks to anthocyanins, most creatures in the animal kingdom are unable to make blue pigments. Any instances of blue coloration you come across in animals are typically the result of structural effects, such as iridescence and selective reflection. Take, for example, the bluejay. This little bird produces melanin, meaning it should technically appear almost black. However, tiny air sacs in the bird's feathers scatter light, making it appear blue to our eyes. This is called Rayleigh scattering, a phenomenon that is also responsible for the age-old " why is the sky blue?" question."
This is also the reason we see so many more blue butterflies and birds than reptiles, amphibians and animals with scales, skin or fur. It's much easier to achieve the appearance of blue through structural effects in scales and feathers. That doesn't mean it only appears in winged creatures. Some frogs and nudibranchs sport brilliant blue coloration, and we can't leave out the beautiful Grand Cayman blue iguana.
But that raises another question: Why are there no blue cats or giraffes, gazelles, rodents or so many other species that can be found anywhere on the planet? Those animals that are able to bend light to make blue will always stand out as something special.