Mimicry (or imitative coloration, is a phenomenon)

MIMICRY, or imitative coloration, is a phenomenon belonging to the category of protective coloration (see Coloration). The concept of M. was first precisely formulated by the English zoologist Bates (1861). M. is defined as the protective value of imitative similarity in external appearance, body form, and coloration between animals that are far removed from each other in the systematic classification. In most cases, the similarity exists between forms that are defenseless by nature on one hand, and animals that possess properties that protect them well from enemies on the other. Thus, combinations are formed of models possessing protective properties and imitators resembling them. The majority of scientists consider M. to be a useful adaptation for the 'imitators' that developed through natural selection. The doctrine of mimicry received further development in the works of Wallace, Trimen, F. Müller, Poulton, and others, who divided this concept into several categories. At present, they distinguish 1) Batesian M.—cases of imitation by defenseless animals of forms that are immune, i.e., possessing protective properties, and 2) Müllerian mimicry, as cases are designated in which there is imitation of immune forms by a single central, also immune species. M. is widespread, especially among terrestrial arthropods and vertebrates. In most cases, both the model and the 'imitator' belong to the same class, and more often even to the same order. However, cases of M. are known between representatives of different classes (for example, between spiders and ants). Among vertebrates, M. is particularly pronounced in some snakes in South America: many species of non-venomous snakes, for example, Homalocranium senicinctum, imitate the very venomous snakes of the genus Elaps ('coral snakes'), which possess a very bright warning coloration of red, black, and white rings. The opinion is fairly widespread, although not sufficiently substantiated, that the cuckoo uses its similarity to the hawk to scare away songbirds and more easily lay 'its eggs in the nests of the latter. There are especially many examples of M. among insects. The models for imitation are primarily various stinging Hymenoptera, namely wasps, bumblebees, and bees, which are imitated by flies and moths (Sesiidae); in the latter, M. is expressed in the body coloration (alternating black and yellow rings, as in wasps), in the loss of scales on the wings, which become transparent like those of the models, and sometimes in the constriction of the abdomen, resembling the waist of wasps. Another group of models is formed by ants, which possess poison glands and a social instinct of mutual aid during attack. Incidentally, insects that live in association with them, symphiles or 'ant guests,' which use shelter and food from the ants, often 'imitate' ants. A third object for 'imitation' are certain beetles and moths that have an unpleasant odor or a poisonous taste. Ants are 'imitated' by some bugs, beetles, and spiders, while moths are only imitated by other moths lacking the aforementioned unpleasant protective properties. M. among butterflies is developed mainly in the tropics, where complex complexes of species related to each other by this phenomenon are often encountered. Thus, the classic example of M. is given by the diurnal butterflies of South America: two groups of immune butterflies, Heliconinae and Ithomiinae, possess striking similarity in coloration and body form, thus showing bright Müllerian M.; but in addition to these forms, a whole complex of non-immune, i.e., defenseless butterflies from the family Pieridae and from the family Saturniidae, dressed in the same costume, are found together with them; consequently they are bound to the first two groups by the ties of Batesian M. The result is, as it were, an extensive 'ring' of butterflies of different families, found in the same locality and united by the phenomenon of mimicry. In addition to the numerous examples of protective M., some scientists recognize the possibility of M. of an aggressive character, i.e., the imitation of some animals (predators or parasites) by others, completely harmless, allowing them to more easily prey upon them under this mask. Thus, the similarity of one American predatory hawk (Accipiter pilcatus) with another insectivorous hawk (Harpago diodon) is explained: under the guise of the latter, Accipiter deceives small birds, which it feeds on. Of the same type is M. in cuckoo bumblebees (Psithyrus); living in the nests of ordinary bumblebees (Bombus), whose food supplies they use to feed their own larvae. Despite the widespread occurrence of M., some scientists, for example, more recently Heikertinger, try to deny its useful significance, attributing the observed coincidences in coloration and body form to purely random character. Eimer and some others explain M. as the result of parallel development of more or less related groups of animals, caused in some cases by the effect of identical environmental conditions on such animals; thus, for example, the origin of South American 'rings' of butterflies is explained. The usefulness of M. is refuted by the considerations that butterflies are generally relatively little pursued by birds, and therefore protective M. in relation to them has little meaning. Moreover, in cases where only one sex possesses imitative coloration, the other, not protected by it, is encountered just as often as the mimetic sex. However, all the above objections give way to the extremely weighty arguments that have been brought in favor of the protective and adaptive significance of M. since the time of Wallace. The main arguments are as follows: 1) 'imitators' always live in the same area as models and are encountered together; 2) 'imitators' are always more defenseless than models; 3) 'imitators' are always less numerous (in terms of the number of individuals) than models, which is a very essential condition for the usefulness of M.; 4) the coloration of mimetic forms more or less sharply deviates from the type of coloration of their non-mimetic close relatives; 5) mimicry is found only in insects flying by day, and particularly often in females, not in males; this becomes understandable when one considers that the protection of females is much more important for the preservation of offspring and continuation of the life of the species than the protection of males.