It has been found that some apparently warningly coloured butterflies and other creatures are palatable to insectivorous animals. The explanation given of this is that these showy but edible butterflies “mimic,” that is to say, have the appearance of, show a general resemblance to, species which are unpalatable. This is known as Batesian mimicry. “Protective mimicry,” writes Professor Poulton (Essays on Evolution, p. 361), “is here defined as an advantageous superficial resemblance of a palatable defenceless form to another that is specially defended so as to be disliked or feared by the majority of enemies of the groups to which both mimic and model belong—a resemblance which appeals to the senses of animal enemies . . . but does not extend to deep-seated characters, except when the superficial likeness is affected thereby.”
As Wallace has pointed out, five conditions must be satisfied before such protective mimicry can occur:—
“1. That the imitative species occur in the same area and occupy the same station as the imitated. 2. That the imitators are always the more defenceless. 3. That the imitators are always less numerous in individuals. 4. That the imitators differ from the bulk of their allies. 5. That the imitation, however minute, is external and visible only, never extending to internal characters or to such as does not affect the external characters.” (Darwinism, Chap. ix.)
Thus the mimic is supposed to deceive his enemies by deluding them into the belief that he is the inedible species which they once tried to eat and vowed never again to touch, so nasty was it. The mimic, then, may be compared to the ass in the lion’s skin. Needless to say, this mimicry is quite unconscious. It is supposed to have been developed by natural selection. Every popular book on Evolution cites many examples of such mimicry. We may therefore content ourselves with mentioning but a few.
Examples of Mimicry
Our common wasps are copied by a beetle (Clytus arietis), active in movement and banded black and yellow, and by several yellow-barred hover-flies (Syrphidæ); and the bumble-bee by a clear-winged moth (Sesia fuciformis). There is, indeed, a whole group of these clear-winged moths, resembling bees, wasps, and other stinging hymenoptera. The common Indian Danaid butterfly, Danais chrysippus, is marvellously reproduced by the female of Hypolimnas misippus, a form allied to our Purple Emperor. The male of this is black, with white blue-bordered patches, the female chestnut, edged with black and with white spots at the tips of the wings, as in the Danais. Finn has shown experimentally that this species is liked by birds.
Another common Indian Danaid (D. limniace), black, spotted with pale green, is imitated, though not very closely, by the female of one of the “white” group, Nepheronia hippia. Finn found that this insect was eaten freely by birds, and that the common jungle-babbler (Crateropus canorus) was deceived by the mimicry of the female. The very nauseous Indian swallow-tail (Papilio aristolochiæ) is closely imitated by another swallow-tail (P. polites), both having black wings marked with red and white; P. aristolochiæ, however, has a red abdomen. This difference was not noticed by two species of Drongo-shrikes (Dicrurus ater and Dissemurus paradiseus), to which the butterflies were offered; but the Pekin robin (Liothrix luteus)—a very intelligent little bird—did not fail to pick out and eat the mimic, though it was deceived by the marvellously perfect imitation of Danais chrysippus, by the female of the Hypolimnas.
Such resemblances can therefore be effective.
The cases of mimicry usually quoted include very few among mammals, probably, as Beddard suggests, because the species of that class are relatively few.
The insectivorous genus Tupaia is supposed to mimic the squirrels, which it much resembles as regards form in all respects save the long muzzle; the idea being that squirrels are so active that carnivorous animals find it hopeless to pursue them.