FIG
1.Papilio merope, male, Africa.
2.The same species, one form of mimetic female.
3.Danais chrysippus, Africa, immune model of Fig. 2.
4.Papilio merope, second form of mimetic female, S. Africa.
5.Amauris niavius, S. Africa, immune model of Fig 4.
6.Papilio merope, third form of mimetic female, S. Africa.
7.Amauris echeria, S. Africa, immune model of Fig. 6.
8.Danais erippus, immune model of Fig. 9, Central N. America.
9.Limenitis archippus, Central N. America, mimics the foregoing species.
10.Danais erippus, (a) CATERPILLAR, (b) PUPA.
11.Limenitis archippus, (a) CATERPILLAR, (b) PUPA.

To face Plate I

This comparative rarity is true of the imitators of the Heliconiidæ and their great mimicry ring of unpalatable species, and is very general. Thus, for instance, there is a series of palatable mimics of the beautiful blue Euplœæ of the Indo-Malayan region ([Pl. III], Figs. 25 and 27), but each of these mimics is rare compared with the hosts of the blue unpalatable company, for these immune butterflies also occur in many species, all similar to Euplœa midamus or binotata ([Pl. II], Figs. 1 and 3); and the same applies to the mimics of the Indo-Malayan Danaidæ. There are a great many Danais species, all of them resembling Danais vulgaris ([Pl. III], Fig. 20), which, when they occur together, form an inedible ring, and this ring is imitated by a whole series of edible species, each of which is comparatively rare. And there are no fewer than six species of Papilio which resemble these Danaids to the point of being easily mistaken for them, while another rare Papilio effectively copies the iridescence of the blue Euplœæ—a coloration so unusual in the genus that the species has received the name of Papilio paradoxus.

But even in single species of butterflies immune through unpalatability there is usually a great abundance of individuals. Thus Danais chrysippus, which is distributed over the whole of Africa, is a very common butterfly wherever it can live at all; and in North America, in which country there are only two widely distributed species of Danais, these often occur in enormous numbers. The beautiful large Danais erippus Cramer ([Pl. I], Fig. 8), is distributed over almost all America, and in many places is not only frequent, but occurs in great swarms. Usually it peoples the broad, open stretches of the western prairies of the United States, but when violent winds blow, as they do there in September especially, the insects are driven together into the small wooded spots of the prairie, and then they cover the trees in incredibly large crowds, often so thickly that the leaves are entirely hidden, and the trees look brown instead of green. Millions of butterflies go to make up such swarms, which have been observed in many parts of the United States, even quite in the East, in New Jersey, and elsewhere.

Considering this extraordinary abundance of the immune species, it is not surprising that its palatable copy, Limenitis archippus ([Pl. I], Fig. 9), should also be widely distributed in North America, and in many places it is not rare, but even abundant. The enormous majority of Danais erippus will protect the species which resembles it so closely, even though it is not rare. Any doubt as to this being a case of mimicry disappears in face of the fact that, in Florida, there flies a second very similar but much darker brown North American Danais, and that it is accompanied there by an equally dark variety of Limenitis archippus (L. eros).

To prove the correctness of the hypothesis of an actual process of selection—which we assume in our interpretation of mimicry—I mean the assumption that the disguise of the species seeking protection really deceives the enemy, and thus actually affords protection, I need only cite the evidence of an acute and experienced entomologist who was himself deceived by it. Seitz[6], to whom we owe many valuable biological observations on butterflies, relates that, while he was collecting in the neighbourhood of the town of Bahia, he was surrounded by swarms of Catopsiliæ, similar to our lemon butterfly, especially the common Catopsilia argante, but he took no notice of these, as he 'had already collected as many of them as he wanted.' It was only when he saw a pair in copula that he caught them in his net. But to his extreme surprise he found that he had not caught a Catopsilia, but a butterfly of the family Nymphalidæ, one of those Anææ whose numerous species are distributed over South America. These Anææ are dark, or beautifully bright on the upper surface, but on the under side are leaf-coloured, and one of them bears the name Anæa opalina, because it is quite clear and pale, and of opal-like brilliance. The captive was nearly related to this species. Seitz was so much surprised by the discovery that the male, which had quickly detached itself from the female, escaped him, and he could only make out that, 'as it flew away, it unfolded dark wings, which certainly bore little resemblance to those of the lemon butterfly.' In the hope of securing more of this rare booty he then hunted only for Catopsilia argante, without however securing another coveted specimen—he caught no more Anœæ, which shows that in this case, too, the mimetic species was much rarer.

[6] In citing this observation of Seitz, I do not mean to assert that there is true mimicry between Anæa opalina, or its allied species in Bahia, and the Catopsilia, though I regard this as extremely probable, because of the marked dimorphism between the male and the female, in conjunction with the very striking resemblance of the female to the Catopsilia. The example was given only to show how very deceptive such resemblances may be. To assert with confidence that it is a case of mimicry we should require to know that Catopsilia is immune, and on that point we have as yet no information.