Blue is one of the rarest colors in nature. Few animal species are naturally blue, and few plants have blue flowers. Early humans even acknowledged and described the color blue much later than other colors (Simonis et al. 2012).
But in the world of frogs, blue is actually a fairly common color!
In most cases, frogs will exhibit blue either to advertise their toxicity to potential predators, or to mimic another species more dangerous than themselves. Some frogs can also turn blue during reproduction, thermoregulate, or to avoid predators.
Even though the color blue may be rare in nature as a whole, it is surprisingly common in frogs, and the reasons for that are as fascinating as the frogs themselves.
Some Frogs Are Naturally Blue
Some frogs are blue because they use a defence mechanism called aposematic coloration in which an animal uses bright, highly-visible coloration, like blue, to warn away potential predators.
But not all aposematism is color-based. Other forms of aposematism include sound, like the rattlesnakes’ use of sound to communicate to potential predators that they are dangerous.
Poison Dart Frogs, including Blue Poison Dart Frogs, are the best-known example of aposematic coloration. Their vibrant, eye-catching colors tell potential predators that these tiny frogs are not a tasty snack, but instead highly poisonous.
Essentially, aposematic coloration is the opposite of camouflage:
- Camouflage helps an animal avoid predators by making the animal look like and blend into their surroundings.
- Aposematic coloration helps an animal avoid predators by standing out and advertising their danger, like a warning sign.
However, not all colorful frogs are poisonous. Some have adapted to use mimicry, in which they have very similar colors and markings to another animal that is dangerous.
A good example of this is the Mimic Poison Frog (Ranitomeya imitator), a dart frog species that has equally bright coloration, but substantially lower levels of toxicity, than other dart frog species.
Studies show that in at least some Poison Dart Frog species, the brightness of the frog’s coloration directly correlates to the level of its toxicity. It was also shown that predators, particularly birds, are able to detect this difference in brightness (Maan et al. 2012).
Bright blue likely stands out to predators due to its relative rarity in nature, making it a good choice for a frog to indicate to predators that they are not a snack.
Even in plants, blue is one of the rarest natural colors. Thus, a blue frog is more likely to stand out than a red or green one that could easily blend in to plant life around them.
Why Can Some Frogs Turn Blue?
Some frogs may turn blue during reproduction, in order to thermoregulate, or to avoid predators.
Some frogs like male Moores Frogs change colours during mating season to distinguish themselves from females.
Some frogs may turn blue due to environmental conditions. In some species and in some circumstances, this darker color may appear blue.
This is a fairly common adaptation throughout the range of ectothermic, or cold-blooded, animals such as amphibians and reptiles.
Since they rely on environmental heat to regulate their own body temperatures, becoming darker is a very effective way to increase the amount of heat they can absorb, and reduce the amount of time that absorption takes. Think about going outside in a black shirt on a hot day- you heat up much faster than if you wore a white shirt.
Frogs can also change colors due to uncomfortable situations. A frog that is stressed, hungry, or cold may change to a darker or duller color than normal which may seem blue in some species.
Some species also exhibit color morphs that cause a normally green frog to become blue. In my experience, I have seen Green Tree Frogs (Hyla cinerea) and Fire-Bellied Toads (Bombina sp.) that are axanthic, or lacking yellow pigments, causing them to appear blue.
Why Do Some Frogs Hide Their Blue Colors?
If you’re familiar with the Red-Eyed Tree Frog (Agalychnis callidryas) you may know that they sleep with their legs tucked into their bodies, and appear fully green. But while awake, they show vibrant blue, yellows, and oranges on their abdomens and legs, and bright red eyes.
This is known as flash coloration. It is effectively a compromise between camouflage and aposematic coloration.
With flash coloration, an animal has an option to be camouflaged and hidden from predators, such as a sleeping Red-Eyed Tree Frog that blends in perfectly with a leaf.
While awake, however, the frog shows bright, vibrant colorations that serve the same purpose as the bright colors of a dart frog- a warning sign to advertise their toxicity to a potential predator.
Another great example of flash coloration is the Fire-Bellied Toad (Bombina sp.). These small aquatic frogs have a muted green back that allows them to be camouflaged if viewed from above while in the water.
However, their bellies have the bright red or orange coloration that gives them the name “Fire-Bellied”. If threatened, these frogs go into a position called the Unkenreflex, in which the body is arched in a way that shows off the bright belly, scaring away a potential predator.
The Unkenreflex is seen in a variety of amphibians, including some species of salamander and newt. This defense can also serve to startle or surprise a potential predator into leaving the animal alone.
This article was written in collaboration with another Master Herpetologist certified by the Amphibian Foundation.
Simonis, P., & Berthier, S. (2012). How nature produces blue colors. Photonic Crystals – Introduction, Applications and Theory. https://doi.org/10.5772/32410
Maan, M. E., & Cummings, M. E. (2012). Poison frog colors are honest signals of toxicity, particularly for bird predators. The American Naturalist, 179(1). https://doi.org/10.1086/663197
King, R. B., Hauff, S., & Phillips, J. B. (1994). Physiological color change in the green treefrog: Responses to background brightness and temperature. Copeia, 1994(2), 422. https://doi.org/10.2307/1446990