Mimicry in Butterflies. Reginald Crundall Punnett
this case later on, and it is sufficient here to call attention to the three different forms of female, of which one is like the male while the other two resemble two other species of Papilio, P. hector and P. aristolochiae, which occur in the same localities. Instances where the female alone of some unprotected species mimics a model with obnoxious properties are common in all tropical countries. It has been suggested that this state of things has come about owing to the greater need of protection on the part of the female. Hampered by the disposal of the next generation the less protected female would be at a greater disadvantage as compared with the mimic than would the corresponding male whose obligations to posterity are more rapidly discharged. The view of course makes the assumption that the female transmits her peculiar properties to her daughters but not to her sons.
A few years later Trimen[5] did for Africa what Bates had done for America and Wallace for Indo-Malaya. It was in this paper that he elucidated that most remarkable of all cases of mimicry—Papilio dardanus with his harem of different consorts, all tailless, all unlike himself, and often wonderfully similar to unpalatable forms found in the same localities (cf. p. 30).
We may now turn to one of the most ingenious developments of the theory of mimicry. Not long after Bates' original memoir appeared attention was directed to a group of cases which could not be explained on the simple hypothesis there put forward. Many striking cases of resemblance had been adduced in which both species obviously belonged to the presumably unpalatable groups. Instances of the sort had been recorded by Bates himself and are perhaps most plentiful in South America between species belonging respectively to the Ithomiinae and Heliconinae. On the theory of mimicry all the members of both of these groups must be regarded as specially protected owing to their conspicuous coloration and distasteful properties. What advantage then can an Ithomiine be supposed to gain by mimicking a Heliconine, or vice versâ? Why should a species exchange its own bright and conspicuous warning pattern for one which is neither brighter nor more conspicuous? To Fritz Müller, the well-known correspondent of Darwin, belongs the credit of having suggested a way out of the difficulty. Müller's explanation turns upon the education of birds. Every year there hatch into the world fresh generations of young birds, and each generation has to learn afresh from experience what is pleasant to eat and what is not. They will try all things and hold fast to that which is good. They will learn to associate the gay colours of the Heliconine and the Ithomiine with an evil taste[6] and they will thenceforward avoid butterflies which advertise themselves by means of these particular colour combinations. But in a locality where there are many models, each with a different pattern and colour complex, each will have to be tested separately before the unpalatableness of each is realised. If for example a thousand young birds started their education on a population of butterflies in which there were five disagreeable species, each with a distinct warning pattern, it is clear that one thousand of each would devote their lives to the education of these birds, or five thousand butterflies in all[7]. But if these five species, instead of shewing five distinct warning patterns, all displayed the same one it is evident that the education of the birds would be accomplished at the price of but one thousand butterfly existences instead of five. Even if one of the five species were far more abundant than the others it would yet be to its advantage that the other four should exhibit the same warning pattern. Even though the losses were distributed pro rata the more abundant species would profit to some extent. For the less abundant species the gain would of course be relatively greater. Theoretically therefore, all of the five species would profit if in place of five distinct warning patterns they exhibited but a single one in common. And since it is profitable to all concerned what more natural than that it should be brought about by natural selection?
Müller's views are now widely accepted by students of mimicry as an explanation of these curious cases where two or more evidently distasteful species closely resemble one another. Indeed the tendency in recent years has been to see Müllerian mimicry everywhere, and many of the instances which were long regarded as simple Batesian cases have now been relegated to this category. The hypothesis is, of course, based upon what appears to man to be the natural behaviour of young birds under certain conditions. No one knows whether young birds actually do behave in the way that they are supposed to. In the absence of any such body of facts the Müllerian hypothesis cannot rank as more than a plausible suggestion, and, as will appear later, it is open to severe criticism on general grounds.
Perhaps the next contribution to the subject of mimicry which must rank of the first importance was that of Erich Haase[8], to whose book students of these matters must always be under a heavy obligation. It was the first and still remains the chief work of general scope. Since Haase's day great numbers of fresh instances of mimetic resemblance have been recorded from all the great tropical areas of the world, and the list is being added to continually. Most active in this direction is the Oxford School under Professor Poulton to whose untiring efforts are largely due the substantial increases in our knowledge of African butterflies contributed by various workers in the field during the past few years. Whatever the interpretation put upon them, there can be no question as to the value of the facts brought together, more especially those referring to the nature of the families raised in captivity from various mimetic forms. With the considerable additions from Africa[9] during the past few years several hundreds of cases of mimicry must now have been recorded. Some of the best known and most striking from among these will be described briefly in the next two chapters.
CHAPTER III
OLD-WORLD MIMICS
The earlier naturalists who studied butterflies made use of colour and pattern very largely in arranging and classifying their specimens. Insects shewing the same features in these respects were generally placed together without further question, especially if they were known to come from the same locality. In looking through old collections of butterflies from the tropics it is not infrequent to find that the collector was deceived by a mimetic likeness into placing model and mimic together. During the last century, however, more attention was paid to the anatomy of butterflies, with the result that their classification was placed upon a basis of structure. As in all work of the sort certain features are selected, partly owing to their constancy and partly for their convenience, the insects being arranged according as to whether they present these features or not. Everybody knows that the butterflies as a group are separated from the moths on the ground that their antennae are club shaped at the end, while those of the moth are generally filamentary and taper to a fine point.
Figs. 1–8. Terminal portion of front legs of butterflies belonging to different families. (After Eltringham.)
| 1. Hypolimnas misippus, | ♀ (Nymphalidae). |
| 2. Hypo"imnas mis" | ♂ (Nymp"alidae). |
| 3. Abisara savitri, | ♀ (Erycinidae). |
| 4. Abi"ara sav" | ♂ (Eryci"idae). |
| 5. Lycaena icarus, | ♀ (Lycaenidae). |
| 6. Cupido zoë, | ♂ (Lyca"nidae). |
| 7. Ganoris rapae, | ♂ (Pieridae). |
| 8. Papilio echerioides, | ♀ (Papilionidae). |
The butterflies themselves may be subdivided into five main groups or families[10] according to the structure of the first of their three pairs of legs. In the Papilionidae or "swallow-tails," the first pair of legs is well developed in both sexes (Fig. 8). In the Pieridae or "whites," the front legs are also similar in both sexes, but the claws are bifid and a median process, the