Mimicry

in zoology, a simulation of something else in form, or color, etc. A measuring worm, the larva of the geometrical moth, on the approach of a footstep will stand out straight from a branch and imitate a twig so perfectly that the observer puts out a finger to touch it to make sure it is not a twig. The thunderpumper or bittern will stand in a swamp with head and neck in a rigor, imitating a weed or tuft of grass till the passer-by is gone. A tree frog has the power of changing color to more closely resemble the surface on which it desires to be inconspicuous. It is said to be able to change its color from a dark hue to a light one in about twenty minutes. This is accomplished by a rearrangement of the pigment in the external cells of the body.

Quite distinct from voluntary mimicry, but often called by the same name, is protective mimicry or protective coloration. The autumn plumage of quails resembles dead grasses and leaves so closely that the hunter may be unable to see a covey less than twenty feet distant. The arctic ptarmigan and the snowy owl in winter plumage are so white that they are invisible against an expanse of snow. The katydid and the green grasshopper are inconspicuous in the growing grass. Gray locusts can scarcely be seen in a dusty plain. The northern hare and the weasel turn white when winter comes. The walking-stick looks like a dead twig; some of the crabs look like stones; the leaf butterfly of India folds its wings so like a leaf of the bush it visits that even a bird is unlikely to see it. These are but a few of the many instances of protective mimicry.

Of course this sort of protection is beyond the power of the animal concerned. It is the result of natural selection carried on for it may be thousands of years. The individuals of a species that most nearly resemble their surroundings are most likely to be overlooked by hungry enemies, and are on that account most likely to be left to produce young to perpetuate the species. If this process of selection be kept up indefinitely, the protective shape or color becomes the standard shape or color of the species.

Although beyond their power to change, animals seem keenly aware of the degree to which their color protects them. One writer speaks of a woodcock that had so great faith in the resemblance of her plumage to the leaves about her, that she would permit the observer to approach within a few feet of the nest before she took wing; but a light snowfall having occurred, this in April, the wary bird made off ere the observer had come within fifty feet of the nest. The whip-poor-will nesting in a footpath sits in confidence, like a fluff of forest leaves, until almost trodden upon.