114 THE EVOLUTION THEORY 



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 

 (PI. 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 protec- 

 tion, I need only cite the evidence of an acute and experienced 

 entomologist who was himself deceived by it. Seitz^, 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 Gatopsilioi, 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 Nymphalidse, 

 one of those Ancuce whose numerous species are distributed over 

 South America. These Ancece are dark, or beautifully bright on the 

 upper surface, but on the under side are leaf-coloured, and one of 

 them bears the name Ancea opalina, because it is quite clear and 

 pale, and of opal-like brilliance. The captive was nearly related to 



' lu citing this observation of Seitz, I do not mean to assert that there is true 

 mimicry between Ancea 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. 



