Mimicry in Butterflies. Reginald Crundall Punnett
Here, so far as is known, occur three forms, all tailed, of which one is similar in general colour and pattern to the male, while the other two, niavioides and ruspina[16], resemble respectively a tailed hippocoon and a tailed trophonius. Lastly we have to record that Papilio dardanus is also found as the geographical race humbloti on Comoro Island, and as meriones on Madagascar. In both forms the females are tailed, and resemble the males.
From this long series of facts it is concluded that the male of P. dardanus represents the original form of both sexes. On the islands of Comoro and Madagascar this state of things still survives. But it is supposed that on the African continent existed enemies which persecuted the species more than on the islands and encouraged the development of mimetic forms in the female. The original female still lingers in Abyssinia though it is now accompanied by the two mimetic forms niavioides and ruspina. Over the rest of the area occupied by dardanus the females are always tailless and, with the exception of trimeni and dionysus, wonderfully close mimics. Trimeni, the intermediate form, provides the clue to the way in which the mimetic females have been derived from the male, viz. by the prolongation across the fore wing of the dark costal bar already found in the females of the Madagascar and Abyssinian races, by the deepening of the dark edging to the wings, and by the loss of the tail. Through the gradual accumulation of small variations trimeni came from the male-like female, and by further gradual accumulation of small favourable variations the mimetic forms came from trimeni. South of the equator the male-like form and the intermediate trimeni have disappeared owing to the stringency of selection being greater. Moreover the likeness of mimic to model is closer than in the north, a further proof of the greater stringency of natural selection in these parts. Such in brief is the explanation in terms of mimicry of the remarkable and complex case of dardanus.
Although the Euploeinae are not represented on the African continent, it is the headquarters of another distasteful family of butterflies—the Acraeinae—which is but sparingly represented in the Oriental region[17]. Of smaller size than the Danaines they are characterised, like this group, by their tenacity of life and by the presumably distasteful character of their body juices. They are said also to possess an offensive odour apparently exuded through the thorax. The majority of the members of the group fall into the two genera Acraea and Planema. Species of Acraea are on the whole characterised by their general bright red-brown colour and by the conspicuous black spots on both fore and hind wings. A typical Acraeine pattern is that of Acraea egina (Pl. VI, fig. 7) which is mimicked remarkably closely by the Nymphaline Pseudacraea boisduvali and by the Swallow-tail Papilio ridleyanus (Pl. VI, figs. 5 and 6).
In the genus Planema the spots are as a rule fewer and clustered near the body, while on both fore and hind wings there is a tendency to develop clear wide band-like areas of orange or white (cf. Pl. VII).
Like the Acraeas the Planemas are principally mimicked by species of Pseudacraea and of Papilio. Some of the cases of resemblance between Planema and Pseudacraea are among the most striking known. Planema macarista is one of those comparatively rare instances in which a model shews a marked difference in the pattern of the two sexes. The clear area on the fore wing of the male is deep orange, whereas in the female it is somewhat different in shape, and, like the area on the hind wing, is white (cf. Pl. VII, figs. 1 and 2). Pseudacraea eurytus hobleyi (Pl. VII, figs. 6 and 7) shews a similar difference in the sexes, the male and female of this species mimicking respectively the male and female of Planema macarista. The case is made even more remarkable by the fact that both of the sexual forms of Planema macarista are mimicked by the Satyrine Elymnias phegea (Pl. VII, fig. 9), though in this species either the black and white, or the black, white, and orange form may occur in either sex. Among the best Papilionine mimics of the Planemas is Papilio cynorta whose female is extraordinarily like the common Planema epaea (Pl. VII, figs. 5 and 10). The resemblance of the planemoides female of P. dardanus to P. poggei has already been noticed.
A striking feature of the African continent is the frequency with which mimetic forms are found among the Lycaenidae. As a rule the "blues" rarely exhibit mimetic analogies, but in Africa there are several species, especially those of the genus Mimacraea, which closely resemble Acraeines. Others again bear a marked resemblance to certain small Pierines, Citronophila similis from S. Nigeria for example being extraordinarily like the common Terias brigitta, a small bright yellow Pierine with black-edged wings.
A remarkable feature of the African continent is the absence of the Pharmacophagus Swallow-tails. Of such Papilios as exhibit mimicry, and as compared with the total number of the group present the proportion is large, the majority resemble one or other of the characteristic Danaines, while a few such as P. ridleyanus and P. cynorta resemble either an Acraeoid or a Planemoid model.
As in the Oriental region the African Pierines do not offer many instances of mimetic analogies. The genus Mylothris, in which certain species are characterised by orange patches at the bases of the undersurfaces of the fore wings, is regarded by some authors as providing models for allied genera such as Belenois and Phrissura. But as neither models nor mimics offer a marked divergence in appearance from the ordinary Pierine facies it is doubtful whether much stress can be laid on these cases.
Africa also offers a few striking instances of mimicry in which day-flying moths play a part. The conspicuous Geometer Aletis helcita is an abundant form, and with its strong red colour and black wing margins broken by white it is a striking object in the preserved state. Among the forms which bear a close resemblance to it are the Nymphaline Euphaedra ruspina, and the Lycaenid Telipna sanguinea[18].
CHAPTER IV
NEW-WORLD MIMICS
Of all the continents South America affords the greatest wealth of butterfly life, and it is in the tropical part of this region that many of the most beautiful and striking cases of mimicry are to be found. Viewed as a whole the butterfly population presents several features which serve to mark it off from that of the other two great tropical areas. In the first place the proportion of gaily coloured forms is higher. Bright red, yellow or fulvous brown contrasted with some deep shade approaching black form the dominant notes. Sombre coloured species are relatively scarcer than in the Oriental and African regions. In the second place when looking over collections from this part of the world one cannot help being struck by the frequency with which similar colour combinations occur over and over again in different as well as in the same groups. Now it is a simple scheme of black with an oblique scarlet band upon the fore wings—now an arrangement with alternating stripes of bright brown and black relieved with patches of clear yellow—now again a scheme of pure transparency and black. Gay and pleasing as are the designs turned out the palette is a small one and invention is circumscribed. Under such conditions it might well be supposed that instances of close resemblance between different species would be numerous, and this in effect is what we find.
As in Asia with its Euploeines and Danaines, and in Africa with its Danaines and Acraeines, so in S. America are the fashions set by two dominant groups of models. These are the Heliconinae and the Ithomiinae, both peculiar to this region and both characterised, like the Old-world Danaids, by slow flight and great tenacity of life. Both live on poisonous plants—the Heliconines on Passifloras and the Ithomiines on Solanaceae. In both groups, but more especially in the Ithomiinae, the species are numerous, and the number of individuals in a species often beyond computation. From the point of view of mimicry these two groups have so much in common that they may conveniently be considered together.
It was from among the Ithomiines, as already pointed out, that the models came for the Pierine mimics of the genus Dismorphia upon which Bates founded the theory of mimicry. Though the Pierine mimics are the most striking the Heliconines and Ithomiines are mimicked by members of other groups. A few Papilios (Pl. X, fig. 8), certain Nymphalines such as Protogonius (Pl. X, fig. 9), Eresia, Phyciodes and Colaenis (Pl. XI, fig. 4), together with various day-flying moths, more particularly of the genera Castnia and Pericopis, are among the well-known