In tropical America the very poisonous snake Elaps ([Plate VI]) is found abundantly. Its style of coloration is very conspicuous and one that does not occur in any other group of snakes, consisting alternately of rings of red, black, and yellow, or red and black of varying width and arranged in different patterns. Snake-eating birds and mammals have learned, through hereditary experiences, to avoid these snakes with gay livery because they are poisonous and therefore dangerous. In [Plate VII] the conspicuously-colored black and yellow salamander is an animal with warning coloration. It is inedible and avoided by carnivorous birds. These warning colorations have been evolved through the Natural Selection of fortuitous useful color variations in the ancestors during the Geologic Ages.
Plate VI.—Illustrating Warning Coloration (Elaps) and especially Mimicry (Erythrolamprus). Elaps is a very poisonous reptile and Erythrolamprus is harmless. Reproduced (and modified) from Romanes’s “Darwin and after Darwin.” By courtesy of the Open Court Publishing Company.
Mimicry. Protective resemblance of a harmless animal to another of a different species that is harmful is known as mimicry. Mimicry is bound up with and altogether dependent upon warning coloration. Some beetles are protected by having integuments, etc., of very great hardness. Several genera of weevils are in this way saved from attack by insect-loving birds. These weevils are often closely imitated in appearance by softer and more eatable species of different genera from the weevils. Wasps and bees are often mimicked by insects of other orders.
Insectivorous birds are very active in hunting out the edible beetles (Longicornia), and everywhere in tropical regions these beetles so closely resemble other insects which are avoided by the birds that the longicorns are very frequently avoided and thus protected.
In tropical America many butterflies (Heliconidæ) are found that possess warning coloration. They possess an offensive taste and odor which almost entirely exempt them from the attacks of insect-eating animals. The insectivorous birds have learned, by transmitted experiences (heredity) to avoid the Heliconidæ. It is an interesting fact that in the same locality with these distasteful butterflies are other species that are very palatable to insectivorous creatures; but they so closely resemble the non-edible species that the birds pass them by, not recognizing their character.
There are some cases of mimicry among birds. There is a genus of large honey-suckers known as friar birds found in the Malay Archipelago. They are noisy and powerful birds which go in small flocks. They have sharp beaks which are long and curved, and also powerful grasping claws. They are perfectly able to defend themselves, often driving away such birds of prey as hawks and crows when they approach them too closely. In the same environment are weak and timid birds known as orioles, which trust chiefly to their retiring habits and concealment for protection. The orioles, although an entirely distinct species from the friar birds, very closely resemble the latter. In each of the great islands of the Malayan Archipelago there is a distinct species of friar birds, and always in the same locality is a species of oriole that exactly mimics it. The separate species often look so thoroughly alike that competent naturalists, prior to a very close examination, have considered them as belonging to the same species.[10]
The most remarkable cases of mimicry are those in which poisonous snakes are mimicked by harmless ones. There is an egg-eating snake in South Africa that possesses neither teeth nor fangs and is not poisonous. It very closely resembles the poisonous Berg adder. When alarmed it still more closely resembles the adder by the habit of flattening its head and darting forward as if to strike an enemy, hissing at the same time.
Plate VII.—An Amphibian (Salamandra maculosa) illustrating Warning Coloration.