Blue is a rare natural color in the animal kingdom. Most blue colorations in animals are structural colors rather than pigments. Structural colors are created when light interacts with nanostructures in feathers, scales, or skin. This makes the blue color appear iridescent and change based on viewing angle. Only a few animals have evolved to naturally produce blue pigments. The most well-known examples of animals with natural blue coloration are certain breeds of parrot, mandrills, some insects, and a handful of sea creatures.
Blue Parrots
Parrots are among the most vibrantly colored birds. Their feathers contain pigments called psittacofulvins, which produce red, yellow, and orange hues. Some parrot species also have the ability to structurally produce blue, green, and violet iridesce due to the light-scattering properties of customized melanin granules present in their feathers. However, very few parrot species can naturally synthesize the pigment complexes necessary to biologically produce the color blue.
The most brilliantly blue parrots are:
- Hyacinth macaw
- Glaucous macaw
- Lear’s macaw
- Blue-throated macaw
These South American macaws have feathers containing a combination of psittacofulvin pigments along with a unique blue pigment made from modified melanin. This gives them bright blue wings and tail feathers, in addition to cobalt blue skin around the eyes and on the facial patch. The blue macaws’ blue hue is among the most vivid found in nature.
Other parrot species with some blue plumage due to structural colors include:
- Blue-and-yellow macaw
- Blue-crowned conure
- Blue-headed parrot
- Blue-fronted Amazon
But their blue iridescence is not as deep or brilliant as the pure blue pigment-producing macaws.
Blue Insects
While common insects like houseflies and ants appear black, some insect species exhibit striking metallic blue coloration. Unlike parrots though, the blue comes from structural colors rather than blue pigments.
Some examples of insects with blue structural coloration include:
- Blue butterflies – The wings contain nanoscale structures that reflect blue wavelengths of light.
- Blue weevils – Small beetles that have bluish scales covering their bodies.
- Blue damselflies – Their wings refract light and can appear blue or green depending on viewing angle.
- Blue metallic wood-boring beetles – Tiny pits in their exoskeletons diffract light to produce a shimmering blue effect.
When illuminated from different angles, these insects can display iridescent greens, violets, and ultraviolet shades along with blue. Their color is not consistent like the uniform blue in macaws.
Blue Arachnids
Spiders are not actually insects, but some tarantula species from South America exhibit blue coloration like many insects. Examples include the cobalt blue tarantula and the sapphire ornamental tarantula. These large spiders have setae or hairs on their bodies that contain nanostructures capable of scattering blue wavelengths of light through structural color production. Under some lighting conditions they can even appear purple. The blue color is thought to serve an aposematic function, warning predators of the tarantulas’ venomous bite.
Blue-Ringed Octopus
While most octopus species can only change color for camouflage or communication via specialized pigment cells called chromatophores, the blue-ringed octopus is one of the only cephalopods capable of producing a true blue pigment. They have unique iridophore cells that reflect blue light using plate-like nanostructures. When threatened, the normally yellowish octopus flashes dozens of electric neon blue rings across its body, warning predators of its venomous neurotoxic bite. Despite growing to only 20 cm long, the striking blue-ringed octopus carries enough venom to kill an adult human.
Mandarinfish
Small freshwater fish called mandarinfish display some of the most brilliant blue colors in nature. These fish have blue, red, orange, and green pigment cells layered under iridescent green, violet, and blue structural colors made from guanine nanocrystals present in their scales. The combination of light-reflecting plates along with actual pigments allows mandarinfish to glow with shifting rainbow hues brighter than a peacock’s feathers.
Blue-Spined Unicornfish
Unicornfish are tropical marine fish found in coral reefs. The most vividly blue species is the blue-spine unicornfish. It has specialized pigment cells called melanophores that contain short-wave light absorbing pigments to produce its uniform blue coloration. Compared to the iridescent blues produced structurally, the unicornfish’s bioluminescent blue hue does not change based on viewing angle. The brilliant blue helps camouflage the fish against the reef landscape.
Blue-Ringed Blue Moray Eel
The blue-ringed moray eel is agrayish serpentine fish that lives in holes in coral reefs. When threatened, it can flash bright neon blue rings along its body as a warning to predators, similar to the blue-ringed octopus. These blue rings are produced by structural coloration rather than blue pigments. The eel’s body contains specialized ichthyophores or thickened skin cells that refract light and change color. By flexing its muscles, the moray can temporarily alter the space between ichthyophores to make the blue rings flash. After the threat goes away, the moray eel’s body returns to its dull gray camouflage.
Blue Damselfish
Damselfish comprise some of the most brightly colored blue reef fish. The blue devil damselfish is almost entirely a deep blue hue. However, like many damselfish, the blue devil’s color comes from a layer of translucent guanine crystals in the skin that reflect blue light, rather than from blue pigments. Other blue damselfish like the neon damsel may appear more green or violet depending on viewing conditions. But the blue devil is an exceptionally vibrant blue across its entire body.
Blue Tang
Perhaps the most popular blue-colored reef fish is the blue tang, best known as Dory from the movie Finding Nemo. Blue tangs have grey-brown bodies but vibrant blue trim around the mouth, tail, fins, and stomach. The blue comes from pigment cells called chromatophores. But the exact hue can range from greenish-blue to deep violet based on the fish’s environment. In captivity, blue tangs often lose their flashy blue colors. The vibrant blue trim allows blue tangs to stay visible to their own schooling group while blending into the reef surroundings.
Blue Lobster
While most lobsters are colored red or green, genetic anomalies can occasionally produce specimens with bright blue shells. Blue lobsters owe their rare coloration to a genetic defect that causes them to overproduce a particular blue protein. Only about 1 in every 2 million lobsters are blue. The odds of finding an ultra-rare blue lobster are estimated to be 1 in 200 million. Their unique color is the result of both a pigment as well as a structural component. The blue lobster’s shell contains the normal red and yellow pigments astaxanthin and beta-carotene, but its genetic mutation prevents the formation of a protein called crustacyanin that would normally bind to astaxanthin and turn the lobster red. This allows the blue lobster’s shell to reflect blue wavelengths instead.
Blue-Spotted Jawfish
Jawfish are small bottom-dwelling fish found in coral reefs and seagrass beds. The blue-spotted jawfish has head and fins covered in brilliant blue spots. These markings are produced by pigment cells called chromatophores that can expand or contract to change the fish’s coloration for camouflage. When relaxed, the blue spots remain vividly visible to allow the jawfish to communicate with others of its own species. But when frightened, the blue spots fade as the chromatophores constrict, helping the jawfish hide among coral until danger passes.
Other Blue Animals
– Blue penguin – This unique penguin species has blue and white plumage. The blue comes from feather structure as well as melanin and carotenoid pigments.
– Blue frog – Native to the rainforests of Suriname, the light blue coloring of the major’s wood frog remains unexplained.
– Blue dragon sea slug – Bold blue markings on this nudibranch are thought to serve as a warning of its toxicity.
– Cynarctus blue wildebeest – Also called the brindled gnu, this African antelope has a dark bluish sheen to its fur.
Conclusion
While most blue animals rely on nanostructures to scatter blue light through structural coloration, parrots, mandrills, some octopus, fish, and a rare blue lobster can biologically synthesize blue pigments. Unique melanin derivatives allow macaws and mandrills to produce their uniform brilliance. More common are iridescent blues that shift color under different light. But only a few species have evolved the complex genetics to create blue coloration from pigments, making them truly unique in the animal kingdom.
| Animal | Blue color from pigment or structural coloration? |
|---|---|
| Hyacinth macaw | Pigment |
| Blue butterfly | Structural |
| Blue-ringed octopus | Pigment |
| Mandarinfish | Both |
| Blue damselfish | Structural |
| Blue lobster | Both |
| Blue-spotted jawfish | Pigment |