The coloration of animals has long been a matter of controversy between the two groups of biologists, the naturalists and the physiologists. The naturalist has maintained that coloration in animals is entirely purposive and that colors and color patterns of animals are produced by some directive force or forces for purposes of security. The physiologists have insisted that all coloration is physiological and that its production, deposition, distribution, and selection have little to do with rendering any special service to animals and little or no connection with extraneous factors. More recently biologists have recognized certain valid claims of both groups.
In general we can say that color is a tremendous subject with chemical, physical, physiological, and behavioristic phases. A discussion of this topic is significant at this time of the year because animals which are exposed to the elements of nature exhibit changes in their appearance as the weather gradually turns from cold to warm.
All of us have seen the green caterpillar and many have undoubtedly wondered why they were green. Green caterpillars usually get their color from the foliage they eat. The larva of the cabbage butterfly is green; but in the adult the color has been found to he due to the presence of water-soluble uric acid in the scales on the wings. In the pupal stage, the rate of metabolism is high; and considerable waste is produced. Urea is a characteristic waste product of animal metabolism; and since there is no anal opening for the discharge of fecal substances in the pupa, some of the urea is secondarily utilized by the developing butterfly. The wing scales of the butterfly are hollow, flattened sacs; and the chemical substances are deposited in them. These suhstances or pigments give to the scales their colors.
We can observe therefore that coloration of the cabbage butterfly is due to its environment and the chemical changes which occur because of this environment.
It has been suggested by some that variations in color of animals may be due to physical factors, such as light, humidity, temperature, and disease. It has been found that Luna moths kept in glass-covered cases exposed to sunlight usually become pale in a few months. Black beetles, however, usually emerge from their pupal cases with a light tan color which is darkened by the action of atmospheric oxygen on the freshly formed chitin of the exoskeleton (exterior skeleton) of the beetle.
Much more could he written about the relations between color and climate, but the naturalist is primarily interested in color from the viewpoint of the human observer who sees an organism in its natural haunts.
Because of the extreme difficulty in describing colors due to the variability of the individual conception of them, biologists have established an international code of colors for world-wide application. The three classifications which we shall discuss are concealing coloration, aggressive coloration, and mimicry and protective resemblance.
Concealing coloration. Concealing coloration is discussed first because this seems to be most common type of coloration. Concealing coloration includes those colors and color patterns which resemble the background or at least part of it. They make their possessors inconspicuous and therefore enable them to escape observation by their enemies. Green caterpillars on green plants; ruffled grouse and quail among dead leaves; the whip-poor-will on a dead log; green katydids among green plants; the leaf-like wings of the praying mantis; the white coats of weasels in winter; the rough, warty, dirt-colored skin of the ground toad; the green back of the green frog, resting on the surface of an algae filled pond; and many others are examples to illustrate how the color patterns of animals make them difficult to see. A few animals like the chameleons (lizards) and flounders (a fish) can change their colors to match or mimic their surroundings. Flounders can imitate the pattern as well as the color of their background. If the flounder is placed on a checker-hoard, it attempts to reproduce the arrangement of the squares on its body.
Aggressive coloration. This type of coloration is possessed by animals which are predators in their habits hut which visually lack the ability to overtake their victims by pursuit. They usually lie in wait for their victims to approach within reach of their seizing apparatus. Leaf mantises, which are poor fliers and slow crawlers, are excellent examples of aggressive coloration. Certain decorator crabs will pluck sponges, kelp, or sea anemones and hold them in their claws before them. They are thus able to advance on their victims behind a protective screen of harmless organisms.
Mimicry and protective resemblance. In this group are those animals which have a coloration similar to some other animal generally avoided by predators, or to parts of plants. The caterpillar of the brimstone moth resembles a twig broken off at the end; and when disturbed, it will extend one end of its body at an angle similar to that of the twigs on the plant. The body form of an insect called the walking stick also mimics the stem of plants. The viceroy butterfly mimics the inedible but beautiful monarch butterfly. This mimicry is so close that birds avoid the viceroy, as they avoid the monarch butterfly. Birds do not eat the monarch butterfly because the monarch feeds on the leaves of the milk-weed plant which are presumably very bitter to the taste.
There are other colors devices in evidence in nature such as the warning device of the skunk, the signal markings of the white-tailed deer, and the courtship colors of birds; but these all reveal the providential father-hand of God as he controls all things. We do not recognize some blind, all-controlling force but we confess and believe that all things work together for the fulfilling of the good pleasure of Jehovah God. When we observe all these things, we say with our church fathers in the Belgic Confession, Article XIII:
This Doctrine (Divine Providence, AL) affords its unspeakable consolation, since we are taught thereby that nothing can befall us (or the whole universe, AL) by chance, but by the direction of our most gracious and heavenly Father; who watches over us with a paternal care, keeping all creatures so under his power, that not a hair of our head (for they are all numbered), nor a sparrow, can fall to the ground, without the will of our Father, in whom we do entirely trust…
Originally published in:
Vol. 18, No. 2, March 1958