Show someone from the southeastern U.S. a red, black, and yellow (or white) banded snake and a large portion of them will recite some version of the well-known rhyme meant to help distinguish Eastern Coral Snakes (Micrurus fulvius) from species with a similar appearance. Red on yellow kill a fellow. Red on black friend of Jack. Even though this provides an oversimplified and not always 100% accurate method for snake identification (you certainly wouldn’t want to apply this to snakes in Central or South America!), it highlights how a harmless species can give predators pause simply by resembling a species that is potentially dangerous. Unless absolutely sure about an identification, handling snakes with this color pattern in parts of North and South America would be a bad idea.
There are many types of mimicry in the animal kingdom. Alligator snapping turtles have a tongue that mimics a worm to lure potential prey items into striking range. Sneaker males imitate females to slip by larger, dominant males and mate with females that have already been claimed by the bigger male. The most common form of mimicry occurs when a species superficially resembles another species. This often occurs in conjunction with aposematic coloration where a species with potent chemical defenses advertises these defenses with bright coloration (e.g., poison dart frogs). This type of warning coloration is common among many different groups of animals and gives a visual cue to predators to stay away from an animal or risk death.
Batesian mimicry occurs when a harmless species (the mimic) has evolved to take advantage of a visual cue given off by another species (the model) that has chemical defenses. A similar appearance to a dangerous species offers the harmless species some protection from predators as they learn to avoid any animal with that particular color pattern. Alternatively, multiple species that all have chemical defenses can resemble one another, increasing the chances that a predator will avoid all animals with a particular color or pattern. This is known as Müllerian mimicry and is commonly observed in stinging wasps and bees, where many species have yellow and black coloration.
In the southeastern U.S., Coral Snakes have a distinct red, yellow, and black banding that advertises the presence of venom to potential predators. Both Scarlet Kingsnakes (Lampropeltis elapsoides) and Scarlet Snakes (Cemophora coccinea) also possess red, black, and yellow or white banding that can closely resemble the appearance of Coral Snakes. Scarlet Kingsnakes are usually the better mimics, although there are regional differences in appearance within the species, and these regional differences can even have effects on predation rates (Harper and Pfennig 2007). A careful observer can generally differentiate between these three species by the order of the bands and the color at the front of the head. Coral Snakes have a black head while their mimics tend to have red on the end of the head. Aberrant individuals can violate these general rules and leaving snakes alone is always the safest course of action.
Scarlet Snakes, Scarlet Kingsnakes, and Eastern Coral Snakes can all be found in similar habitats, but both Scarlet Kingsnakes and Scarlet Snakes have a much larger overall range than their venomous counterpart. Mimicry is most effective where the model species is present and common enough that predators know to avoid them. In fact, attempted predation attempts on ringed model snakes were higher in portions of the Scarlet Kingsnake range where coral snakes were absent when compared to regions where both species occur (Pfennig et al. 2001). These differences in observed ranges and a low abundance of coral snakes in parts of their range have led some herpetologists to wonder whether or not red and black banding in harmless snakes is truly a case of Batesian mimicry.
Recent research by Rabosky et al. (2016) set out to test whether or not mimicry of coral snakes in the Americas represents an example of Batesian mimicry when examining the entire snake fauna of the region. Using distributional, phenotypic, and phylogenetic data, the authors conclude that there is strong evidence supporting the hypothesis that red and black banding in snakes in the Americas is an example of Batesian mimicry. Interestingly, the data also suggested that banding coloration has been gained and lost on multiple occasions through the evolutionary history of these species. This result was unexpected and has not been observed before in other systems with Batesian mimicry, challenging the assumption that once mimicry is obtained it is unlikely to be lost. Overall, Rabosky et al. (2016) point out that understanding color polymorphism, especially across a large snake assemblage, is a complex task, and there are likely multiple ecological forces at work shaping the distribution of different color morphs.
Regardless of the evolutionary history and ecological process at work, one thing is certain. The warning coloration in coral snakes and subsequent mimicry by other species has produced some of the most visually striking snakes in the southeastern U.S. In southern Georgia where coral snakes and scarlet kingsnakes occur at low densities, sightings of these species are few and far between. It is therefore always a special day when encountering a flash of red, black, and yellow banding in the sandhills of Georgia’s Coastal Plain!
- Harper, G. R., and D. W. Pfennig. 2007. Mimicry on the edge: Why do mimics vary in resemblance to their model in different parts of their geographical range? Proceedings of the Royal Society B: Biological Sciences 274:1955–1961.
- Pfennig, D.W., W. R. Harcombe, and K. S. Pfennig. 2001. Frequency-dependent Batesian mimicry: Predators avoid look-alikes of venomous snakes only when the real thing is around. Nature 410:323.
- Rabosky, A. R. D., C. L. Cox, D. L. Rabosky, P. O. Title, I. A. Holmes, A. Feldman, and J. A. McGuire. 2016. Coral snakes predict the evolution of mimicry across New World snakes. Nature Communications 7:11484.