CHAPTER XII

PROTECTIVE RESEMBLANCES, AND MIMICRY

10%. Protective resemblance defined.—If a grasshopper be startled from the ground, you may watch it and determine exactly where it alights after its leap or flight, and yet, on going to the spot, be wholly unable to find it. The colors and marking of the insect so harmonize with its surroundings of soil and vegetation that it is nearly indistinguishable as long as it remains at rest. And if you were intent on capturing grasshoppers for fish-bait, this resemblance in appearance to their surroundings would be very annoying to you, while it would be a great advantage to the grasshoppers, protecting some of them from capture and death. This is protective resemblance. Mere casual observation reveals to us that such instances of protective resemblance are very common among animals. A rabbit or grouse crouching close to the ground and remaining motionless is almost indistinguishable. Green caterpillars lying outstretched along green grass-blades or on green leaves may be touched before being recognized by sight. In arctic regions of perpetual snow the polar bears, the snowy arctic foxes, and the hares are all pure white instead of brown and red and gray like their cousins of temperate and warm regions. Animals of the desert are almost without exception obscurely mottled with gray and sand color, so as to harmonize with their surroundings.

In the struggle for existence anything that may give an animal an advantage, however slight, may be sufficient to turn the scale in favor of the organism possessing the

advantage. Such an advantage may be swiftness of movement, or unusual strength or capacity to withstand unfavorable meteorological conditions, or the possession of such color and markings or peculiar shape as tend to conceal the animal from its enemies or from its prey. Resemblances may serve the purpose of aggression as well as protection. In the case of the polar bears and other predaceous animals that show color likenesses to their surroundings, the resemblance can better be called aggressive than protective. The concealment afforded by the resemblance allows them to steal unperceived on their prey. This, of course, is an advantage to them as truly as escape from enemies would be.

We have already seen that by the action of natural selection and heredity those variations or conditions that give animals advantages in the struggle for life are preserved and emphasized. And so it has come about that advantageous protective resemblances are very widespread among animals, and assume in many cases extraordinarily striking and interesting forms. In fact, the explanation of much of the coloring and patterning of animals depends on this principle of protective resemblance.

Before considering further the general conditions of protective resemblances, it will be advisable to refer to specific examples classified roughly into groups or special kinds of advantageous colorings and markings.

108. General protective or aggressive resemblance.—As examples of general protective resemblance-that is, a general color effect harmonizing with the usual surroundings and tending to hide or render indistinguishable the animal -may be mentioned the hue of the green parrots of the evergreen tropical forests; of the green tree-frogs and treesnakes which live habitually in the green foliage; of the mottled gray and tawny lizards, birds, and small mammals of the deserts; and of the white hares and foxes and snowy owls and ptarmigans of the snow-covered arctic regions. Of the same nature is the slaty blue of the

gulls and terns, colored like the sea. In the brooks most fishes are dark olive or greenish above and white below. To the birds and other enemies which look down on them from above they are colored like the bottom. To their fish enemies which look up from below, their color is like the white light above them, and their forms are not clearly seen. The fishes of the deep sea in perpetual darkness are

inky violet in color below as well as above. Those that live among sea-weeds are red, grass-green, or olive, like the plants they frequent. General protective resemblance is very widespread among animals, and is not easily appreciated when the animal is seen in museums or zoological gardens-that is, away from its natural or normal environment. A modification of general color resemblance found in many animals may be called variable protective resemblance. Certain hares and other animals that live in northern latitudes are wholly white during the winter when the snow covers everything, but in summer, when much of the snow melts, revealing the brown and gray rocks and

withered leaves, these creatures change color, putting on a grayish and brownish coat of hair. The ptarmigan of the Rocky Mountains (one of the grouse), which lives on the snow and rocks of the high peaks, is almost wholly white in winter, but in summer when most of the snow is melted its plumage is chiefly brown. On the campus at Stanford University there is a little pond whose shores are covered in some places with bits of bluish rock, in other places with bits of reddish rock, and in still other places with sand. A small insect called the toad-bug (Galgulus oculatus) lives abundantly on the banks of this pond. Specimens collected from the blue rocks are bluish in color, those from the red rocks are reddish, and those from the sand are sand-colored. Such changes of color to suit the changing surroundings can be quickly made in the case of some animals. The chameleons of the tropics, whose skin changes color momentarily from green to brown, blackish or golden, is an excellent example of this highly specialized condition. The same change is shown by a small lizard of our Southern States (Anolius), which from its habit is called the Florida chameleon. There is a little fish (Oligocottus snyderi) which is common in the tide pools of the bay of Monterey, in California, whose color changes quickly to harmonize with the different colors of the rocks it happens to rest above. Some of the treefrogs show this variable coloring. A very striking instance of variable protective resemblance is shown by the chrysalids of certain butterflies. uralist collected many caterpillars of a certain species of

An eminent English nat