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Mimicry

Mimicry, a term introduced by Bates in 1862 to denote that close external likeness which causes animals quite distinct to be mistaken for eacli other. The fact of such resemblances among British and European insects had long been known, and had found expression in specific and popular names, e.g. crabroniformis (resembling a hornet), Hornet-moths, Wasp-flies, etc., but no theory as to the reason of such resemblances was advanced. While exploring the Amazon Bates noticed that the butterflies of the families Heliconidaj and Dana'idae were closely m imicked by some of those of the family Pieridae, and that this resemblance was general, not special - i.e. that the Pieridee resembled other (not new) species of the other families inhabiting the same locality. He observed (and in this he was confirmed by Wallace) that the mimicked families were not attacked by birds, lizards, or insects; and in his famous paper on the subject he laid down the two propositions: (1) That the form mimicked has some special protection (as a nauseous taste or smell), or some means of defence (as a sting), and (2) that it is more abundant than the mimickers, which are eatable and defenceless. When more material had been accumulated, Wallace formulated laws adopting Bates's propositions, and adding the following: (1) That the areas inhabited by mimickers and mimicked are the same, (2) that the mimickers differ from the bulk of their allies, and somewhat simplified Bates's definition as to the resemblance being only external. These laws were based on observations made on insects, and to them only do they in strictness apply. But mimicry exists among much higher animals, and the general principle is the same that of protection of some kind. The colouring of the venomous Flaps of Mexico is mimicked by the innocuous Pilocercus, with the same habitat. Our own cuckoo mimicks the plumage of the hawk, and one genus is called Hawk-Cuckoo; and the resemblance of the Aardwolf (Proteles lala.ndii) to the Striped Hyena is probably a case of protective mimicry. It must be remembered that the term "mimicry" implies no conscious imitation, and Wallace believes that the resemblances arose by means of natural selection. But since Bates and Wallace wrote, other investigators have carried the matter farther, as will be seen from the following scheme of animal coloration condensed from the paper of Mr. Poulton, F.R.S., read before the British Association at Leeds in 1890 :

I. CRYPTIC COLOURS (for concealment).

1. Pbocbyptic (protective). The green pipe-fish is well concealed among zostera leaves, but conspicuous in clear water.

2. Anticryptic (aggressive). The South American horned frog buries itself in the earth, with the colour of which it harmonises, and seizes small animals as they approach.

3. Allocryptic (protective and aggressive). Small crabs deck themselves with seaweed.

II. SEMATIC COLOURS (warning and signalling).

1. Aposematic. The brilliant coloration of nauseous insects and the black-and-white coloration of skunks (which emit an intolerable stench).

2. Episematic (serving for recognition). The white scut of the rabbit and the white marks on the hind-quarters of deer and antelopes.

3. Allosematic (in which the warning colour or noxious quality belongs to another animal). Hermit crabs protect themselves by having sea anemones as commensals. He then defines mimicry as "false warning or signalling colours, repelling enemies by the deceptive suggestion of some unpleasant or dangerous quality, or attracting prey by the deceptive appearance of something attractive to them." Even foreign objects commonly associated with some well-defended and agressive species may be mimicked by a comparatively defenceless form.

1. Pseudaposematic (protective). The mimicry nf Bates and Wallace as described above.

2. Psetjdepisematic (aggressive and alluring). The flies of the genus Volucella so closely resemble humble-bees that they lay their eggs in the nests of the latter insects without detection, and their larvae feed on those of the bees. The angler-fish, which attracts other fish by its mouth filaments, is an example of alluring mimicry.

3. Psecdallosematic (the use of foreign objects for concealment). Mr. W. L. Sclater (Proceedings of the Zoological Society, 1891, p. 462) records the fact that an immature homopterons insect in South America mimics the leaf-carrying ant and the leaf it carries.