Mimicry and Illusion: How the Kingsnake Tricks Its Predators
“Red on Yellow Deadly Fellow, Red on Black Friend of Jack.” To anyone who has spent time in the Southern United States, this rhyme will be familiar. Often told to children, it actually serves a very important purpose. Throughout the South, coral snakes scour the undergrowth for prey. While many different species exist within the United States, all share the characteristic red bands flanked by two yellow bands.
This common mnemonic device allows people to distinguish venomous snakes from the many nonvenomous lookalikes. And some of those lookalikes might be very convincing unless you look closely. For example, take a look at the above pictures. At first glance, they appear almost identical. But one is the Eastern coral snake, a highly venomous reptile, whose venom can cause paralysis and respiratory failure in humans. The other is a scarlet kingsnake, which is essentially harmless to humans. If you look quickly at a scarlet kingsnake, you might mistake it for its more dangerous counterpart. But invoking the rhyme, and looking closely, you can see that their red bands only ever touch black ones.
While mutations, like albinism and melanism, can change the look of any snake, the common coloration of the scarlet kingsnake offers a great example of “Batesian mimicry” - where a perfectly edible organism avoids predation by looking like a poisonous one. These kingsnakes avoid being swept off the ground in the talons of an owl or ripped to shreds by the teeth of a coyote because of how similar they look to far more deadly snakes.
This whole relationship depends upon the bright colors of the coral snake. Coral snakes exhibit aposematism - when an organism advertises its toxicity to predators with bright, contrasting colors. Those striking patterns make an organism more visible to predators, which at first seems like a drawback. But, when combined with toxicity, this drawback becomes a benefit. When a toxic organism is easily recognizable, it only takes one bad experience for a predator to learn to avoid them completely. Since the kingsnake co-opted this coloration, it gains all of the benefits of aposematic coloring without actually being toxic.
But how does this mimicry arise in a species? In a paper published in the Proceedings Of The Royal Society, biologists David W. Pfennig and Sean P. Mullen propose a few avenues. First, they suggest that edible species which overlap in range with a toxic one will eventually evolve Batesian mimicry. Since predators relate a specific pattern of bright colors with poison, many will avoid a mimic snake that somewhat resembles the toxic one, while killing the less convincing mimics. Over time, as the arms race between predator and prey continues, mimics become less distinguishable from the real toxic organism, as the obvious fakes die off.
However, not all mimics are equal. In some species, the mimicry is less developed, yet equally as effective against predators. Scientists call this imperfect Batesian mimicry. In their experiment published in the Proceedings Of The Royal Society, L. Lindström, R. V. Alatalo, and J. Mappes proved that the distastefulness of the toxic organism is directly related to the survival rate of the mimic, and indirectly rated to the accuracy of the mimic. The more deadly the aposematic organism is, the less likely a predator is going to risk possibly eating one instead of a mimic. Mimics of such deadly species have less evolutionary pressure to improve their mimicry, and can therefore get away with a less convincing look. This is why the kingsnakes do not have the exact same pattern as the coral snakes. The truly toxic snakes are so dangerous, that predators simply will not take a chance.
The deception of the kingsnake’s patterning does not end here, though. Pfennig and Mullen propose a different origin for the mimicry of the kingsnake, known as “disruptive coloration.” When the snakes slither quickly over a rough background, their bands produce an illusion that makes their outline more difficult to discern. This prevents predators from pinpointing their location while the snakes move. This is the same reason why leopards possess blotched pelts, except the leopards hide from their prey, not their predators. Luckily for the kingsnake, when they cross into the ranges of the poisonous coral snakes, their coloration also protects them from predators who assume they are venomous. Ultimately their mimicry came as a byproduct of the original pressure to not be seen.
This theory is backed up by the distribution of these snakes. Predictably, the scarlet kingsnake exists everywhere that the coral snake does. But it also lives farther north, where no coral snakes exist. If their coloration’s only use was Batesian mimicry, the snakes would not survive outside of the coral snake’s distribution. If predators never learn to avoid the poisonous snakes, the colorful pattern of the scarlet kingsnake would only broadcast its location. Instead, the colors must help it survive in another way, such as disruptive coloration.
Now, you should never approach a snake, whether it is a deadly fellow or a friendly jack. Snakes do not want to harm humans but will strike if provoked. Wildlife is best left alone, and appreciated from a distance. But, if you find yourself bitten by a colorful, banded snake, remember this rhyme, because it might just save you a hospital visit.
