Living Habits of Reptiles (Part 11)

Many kinds of harmless snakes do vibrate their tails when approached by a potential enemy. But in this particular case, what they do cannot possibly be regarded as mimicry. The wide distribution of the trait suggests that snakes were vibrating their tails to scare off enemies long before there were any rattlesnakes in the world. So what rattlesnakes have done is simply to refine and elaborate an adaptation already entrenched in various snake lines. To be sure, some reinforcement of the widespread tail-shaking habit may occur in snakes living in rattlesnake territory, if only because the rattlesnakes buzz so well and because they back up the warning with such deadly effect. But to think that a black snake is mimicking a rattlesnake when it vibrates its tail is to be altogether too credulous.

One of the sources of controversy is the anthropocentric sound of the word mimicry. The verb “mimic” seems to some people to carry a taint of volition, and this colours their appraisal of alleged cases of mimicry and makes them suspicious that these are figments of non-objective interpretation of nature. One of the controversial cases in which even herpetologists are split into camps is that of the so-called mimicking of the gaudily ringed poisonous American coral snakes by various harmless species. Although often referred to as mimicry, some zoologists regard these resemblances as examples of convergent evolution, in which the coral snakes and their non-poisonous counterparts have developed similar colour patterns for some utilitarian reason not connected with warning at all. Some even say that the duplication of pattern is simple coincidence. To support this view it is pointed out that most mammal predators of snakes are colour blind, and would evidently not be able to see the ringed pattern as a particularly striking decoration. Moreover, the striped snakes are all partly subterranean, spending most of their time beneath logs, in old stumps or actually underground, where visual warnings are useless. Still another objection is the occurrence of the ringed coral-snake pattern in harmless snakes living in places where there are no poisonous species around, and hence no conceivable advantage to the deception.

To be continued…

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