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Tricolor snake coloration

Hi everyone, this is Evan again from the Herpetology Team. Over the last several months, I have become very interested in the mimicry of snakes, particularly with tricolor snakes, and what the reasons could be that this tricolor pattern is so often selected for. Here in Georgia, we have a venomous snake called the eastern coral snake. This species is not a viper like the rest of our venomous snakes; it is an elapid, which means they are in the same group as cobras and mambas! Currently there are 88 recognized species of coral snakes in the New World, with many of them featuring a tricolor coloration. This tricolor pattern is typically red, black, and white or yellow bands that alternate each ring. These bright colors are thought to be a warning to predators, something called aposematic coloration. There is a saying that you may have heard that goes, “red touch black, friend of jack, red touch yellow, kill a fellow.” While this saying could certainly be true, it is best to not use this saying as it does not hold true in most places, and if you are ever uncertain, best practice is to leave the snake alone. This phrase arises from the fact that despite the 88 coral snake species, there are countless others that mimic that tricolor pattern.

Historically, the tricolor pattern was thought to be a direct mimic of the coral snakes so that the nonvenomous tricolor snakes would be predated less often. This form of mimicry is called Batesian mimicry. Here in Georgia, we have several species of completely harmless coral snake mimics that fit this mold. We have the scarlet snake, eastern milk snake, and the scarlet kingsnake. The idea that these snakes are mimicking the coral snake, and that is the selective pressure of being tricolor, seems like a very straightforward idea. This is until you realize that there are tricolor snakes outside of the ranges of coral snakes in the New World. The California mountain kingsnake is a great example, as it has a perfect tricolor appearance despite not sharing any of its range with a coral snake.

To get to the bottom of this, you must look at a few other key factors. First is something called flicker-fusion. This is when you have flickering light that reaches a speed where the object seems stationary. The different alternating bands of tricolor snakes create flicker-fusion when the snake is fleeing from predators and can cause them to look like they aren’t moving, allowing them to escape. There are many other banded snake species that play into this that aren’t tricolor, such as the California kingsnake, proving there is a selective pressure for these bands. Secondly, one must look at the ecology of these snakes to better understand their coloration. Coral snakes, as well as all the mimics I have mentioned, are nocturnal or crepuscular, active at dawn or dusk. In limited to no light, these brightly colored snakes no longer appear red, black, and white or yellow. Instead, they are three different shades of grey. Many of their predators that hunt them in these times evolved to not see in color due to the low light. Therefore, this aposematic coloration is not functioning in the way we humans see them and is no longer displaying a warning. The grey will just be camouflaged to their grey surroundings. To summarize, these flashy, tricolor snakes that seem so out of place in nature do, in fact, have evolutionary forces beyond a warning. Next time you see a red, black, and white snake, you can admire the amount of evolution that went into the beautiful coloration!

(Photo: California mountain kingsnake, courtesy of Kelly G.)

Evan H.
Keeper I, Herpetology

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