148
COLOURS
OF
only first become aware of the unpleasant quality by tasting and often destroying their prey; but the species would gain by the experience thus conveyed, even though the individual might suffer. An insect-eating animal does not come into the world with knowledge: it has to be educated by experience, and Warning Colours enable this education as to what to avoid to be gained by a small instead of a large waste of life. Furthermore, great tenacity of life is usually possessed by animals with Warning Colours. The tissues of Aposematic insects generally possess great elasticity and power of resistance, so that large numbers of individuals can recover after very severe treatment. The brilliant Warning Colours of many caterpillars attracted the attention of Darwin when he was thinking over his hypothesis of sexual selection, and he wrote to Wallace on the subject (Darwin, Life and Letters, London, 1887, vol. iii. p. 93). Wallace, in reply, suggested their interpretation as Warning Colours, a suggestion since verified by experiment {Proc. Ent. Soc. Lond., 1867, p. Ixxx • Trans. Ent. Soc. Lond., 1869, pp. 21 and 27). Although animals with Warning Colours are probably but little attacked by the ordinary enemies of their class, they have special enemies which keep the numbers down to the average. Thus the cuckoo appears to be an insectivorous bird which will freely devour conspicuously coloured unpalatable larvae. The effect of the Warning Colours of caterpillars is often intensified by gregarious habits. Another Aposematic use of colours and structures is to divert attention from the vital parts, and thus give the animal attacked an extra chance of escape. The large, conspicuous, easily torn wings of butterflies and moths act in this way, as is found by the abundance of individuals which may be captured with notches bitten symmetrically out of both wings when they were in contact. The eyespots and “ tails ” so common on the hinder part of the hind wing, and the conspicuous apex so frequently seen on the fore wing, probably have this meaning. Their position corresponds to the parts which are most often found to be notched. In some cases (e.</., many Lycoenidce) the “ tail ” and eye-spot combine to suggest the appearance of a head with antenna) at the posterior end of the butterfly, the deception being aided by movements of the hind wings. The flat-topped “ tussocks ” of hair on many caterpillars look like conspicuous fleshy projections of the body, and they are held prominently when the larva is attacked. If seized, the “ tussock ” comes out, and the enemy is greatly inconvenienced by the fine branched hairs. The tails of lizards, which easily break off, are to be similarly explained, the attention of the pursuer being probably still further diverted by the extremely active movements of the amputated member. Certain crabs similarly throw off their claws when attacked, and the claws continue to snap most actively. The tail of the dormouse, which easily comes off, and the extremely bushy tail of the squirrel, are probably of use in the same manner. Animals with Warning Colours often tend to resemble each other superficially. This fact was first pointed out by H. W. Bates in his paper on the Theory of Mimicry {Trans. Linn. Soc. vol. xxiii., 1862, p. 495). He showed that the conspicuous, presumably unpalatable, tropical American butterflies, belonging to very different groups, which are mimicked by others, also tend to resemble each other, the likeness being often remarkably exact. These resemblances were not explained by his theory of Mimicry, and he could only suppose that they had been produced by the direct influence of a common environment. The problem wTas solved in 1879 by Fritz Muller (see Proc. Ent. Soc. Lond., 1879, p. xx), who suggested that life is saved by this resemblance between Warning Colours, inasmuch as the
A.NIMA.LS
[bionomics.
education of young inexperienced enemies is facilitated. Each species which falls into a group with Common Warning {Synaposematic) Colours contributes to save the lives of the other members. It is sufficiently obvious that the amount of learning and remembering, and consequently of injury and loss of life involved in the process, are reduced when many species in one place possess the same Aposematic colouring, instead of each exhibiting a different “danger-signal.” These resemblances are often described as “ Mullerian Mimicry,” as distinguished from true or “ Batesian Mimicry ” described in the next section. Similar Synaposematic resemblances between the specially protected groups of butterflies were afterwards shown to exist in tropical Asia, the East Indian Islands, and Polynesia by F. Moore {Proc. Zool. Soc., 1883, p. 201), and in Africa by E. B. Poulton {Report Brit. Assoc., 1897, p. 688). B. Meldola (Ann. and Mag. Nat. Hist, x., 1882, p. 417) first pointed out and explained in the same manner the remarkable general uniformity of colour and pattern which runs through so many species of each of the distasteful groups of butterflies; wThile, still later, Poulton (Proc. Zool. Soc., 1887, p. 191) similarly extended the interpretation to the Synaposematic resemblances between animals of all kinds in the same country. Thus, for example, longitudinal or circular bands of the same strongly contrasted colours are found in species of many groups with distant affinities. Certain animals, especially the Crustacea, make use of the special defence and Warning Colours of other animals. Thus the English Hermit-crab, Pagurns bernhardus, commonly carries the Sea-anemone, Sagartia parasitica, on its shell; while another English species, Pagurus prideauxii, inhabits a shell which is invariably clothed by the flattened Adamsia palliata. The white patch near the tail which is frequently seen in the gregarious Ungulates, and is often rendered conspicuous by adjacent black markings, probably assists the individuals in keeping together; and appearances with probably the same interpretation are found in many birds. The white upturned tail of the rabbit is probably of use in enabling the individuals to follow each other readily. The difference between a typical Aposematic character appealing to enemies, and Episematic intended for other individuals of the same species, is well seen when we compare such examples as (1) the huge banner-like white tail, conspicuously contrasted with the black or black and white body, by which the slow-moving skunk warns enemies of its power of emitting an intolerably offensive odour; (2) the small upturned white tail of the rabbit, only seen when it is likely to be of use and when the owner is moving, and, if pursued, very rapidly moving, towards safety. Mimicry, or Pseudo-sematic Colours.—The fact that animals with distant affinities may more or less closely resemble each other was observed long before the existing explanation was possible. Its recognition is implied in a number of insect names with the termination -formis, usually given to species of various Orders which more or less closely resemble the stinging Hymenoptera. The usefulness of the resemblance was suggested in Kirby and Spence’s Introduction to Entomology, London, 1817, vol. ii. p. 223. H. W. Bates (Trans. Linn. Soc. vol. xxiii. 1862, p. 495) first proposed an explanation of Mimicry based on the theory of Natural Selection. He supposed that every step in the formation and gradual improvement of the likeness occurred in consequence of its usefulness in the struggle for life. The subject is of additional interest, inasmuch as it was one of the first attempts to apply the theory of Natural Selection to a large class of phenomena up to that time well known but unexplained. Numerous
