Green is an unusual color in the animal kingdom. While many creatures can appear green due to camouflage or diet, truly green animals are rare. Green pigmentation comes from biliverdin, a green tetrapyrrole pigment, or chlorophyll, the green photosynthetic pigment found in plants. Some insects, amphibians, fish, reptiles, and birds exhibit green coloration for camouflage, but very few vertebrate species are naturally and permanently green.
Green insects
Some insects like praying mantises and katydids have green coloration for camouflage. This green comes from pigments like chlorophyll and carotenoids in their exoskeletons. Other insects like emerald cockroaches may appear green but actually have no green pigment. Their iridescent exoskeletons reflect light to produce green hues. Here are some examples of naturally green insects:
| Insect | Mechanism of Green Color |
|---|---|
| Praying mantis | Green pigments like chlorophyll in exoskeleton |
| Katydid | Green pigments like chlorophyll in exoskeleton |
| Emerald cockroach | Structural color from iridescent exoskeleton |
Green amphibians
Several species of frog exhibit green coloration. The most well-known is the green tree frog. This frog’s green skin comes from a blue pigment combined with yellow, which results in green. Some poison dart frogs also exhibit green skin, which serves as a warning to predators of their toxicity. Here are some naturally green amphibians:
| Amphibian | Mechanism of Green Color |
|---|---|
| Green tree frog | Blue and yellow pigments |
| Green and black poison dart frog | Blue and yellow pigments |
Green fish
While uncommon, some species of bony fish are naturally green. The green swordtail gets its color from dietary carotenoids. Gobies may appear green but this comes from reflected light, not pigmentation. Other fish like blennies and wrasses can rapidly change color to blend into their surroundings. Here are some examples of green fish:
| Fish | Mechanism of Green Color |
|---|---|
| Green swordtail | Dietary carotenoids |
| Emerald goby | Structural color |
| Blenny | Color change for camouflage |
Green reptiles
Very few reptiles are naturally green. One exception is the green sea turtle, which has green fat and connective tissue under its shell and skin, likely due to the algae it consumes. Young green anacondas are also green, but this fades to black as they mature. Other reptiles like chameleons and anoles can actively change color for camouflage or signaling. Here are some examples:
| Reptile | Mechanism of Green Color |
|---|---|
| Green sea turtle | Dietary algae |
| Juvenile green anaconda | Unknown pigments |
| Chameleon | Color change for camouflage |
Green birds
Parrots are the main birds that exhibit green plumage. This color comes from psittacofulvins, red and yellow pigments unique to parrots. The green pigments are present in feather structures called melanosomes. Other birds like turacos have green feathers due to copper minerals in their diets. No songbirds or passerines have naturally green coloration. Here are some green birds:
| Bird | Mechanism of Green Color |
|---|---|
| Green parakeet | Psittacofulvin pigments |
| Turaco | Dietary copper minerals |
Mammals
No mammals are naturally green. While some frogs and lizards are green, no salamanders exhibit this coloration. Spider monkeys appear greenish but this comes from the reflection and scattering of light, not true pigmentation. No evidence exists of genuinely green mammals.
Why is green rare in vertebrates?
So why is vibrant green coloration so rare in vertebrate animals? First, green pigments like biliverdin are difficult to produce through metabolism. Often blue pigments must be combined with yellow to make green. Second, most mammals lack green photoreceptor cells, so green blends into background foliage for them. This makes green ineffective for visual communication compared to red or yellow. Lastly, vertebrates lack the highly organized nanostructures that produce structural green color like in insects. So metabolic and physiological constraints prevent widespread green coloration in vertebrates.
Conclusion
While many animals like lizards and frogs can appear green, genuinely green coloration is rare in the vertebrate world. Truly green animals are mostly limited to some insects, fish, turtles, and parrots. Metabolic costs, visual perception, and structural limitations prevent green pigmentation from evolving in most vertebrate groups. So next time you see a vivid green animal, know that it’s a rarity in the kingdom Animalia!
