It is, however, very doubtful whether these are its chief enemies, and its protective form and colour may be needed against insectivorous birds or mammals.
Mr.Samuel H.Scudder, who has largely bred North American butterflies, has found so many of the eggs and larvae destroyed by hymenopterous and dipterous parasites that he thinks at least nine-tenths, perhaps a greater proportion, never reach maturity.

Yet he has never found any evidence that such parasites attack either the egg or the larva of the inedible Danais archippus, so that in this case the insect is distasteful to its most dangerous foes in all the stages of its existence, a fact which serves to explain its great abundance and its extension over almost the whole world.[96] One case has been found of a protectively coloured larva,--one, moreover, which in all its habits shows that it trusts to concealment to escape its enemies--which was yet always rejected by lizards after they had seized it, evidently under the impression that from its colour it would be eatable.

This is the caterpillar of the very common moth Mania typica; and Mr.Poulton thinks that, in this case, the unpleasant taste is an incidental result of some physiological processes in the organism, and is itself a merely useless character.

It is evident that the insect would not conceal itself so carefully as it does if it had not some enemies, and these are probably birds or small mammals, as its food-plants are said to be dock and willow-herb, not suggestive of places frequented by lizards; and it has been found by experiment that lizards and birds have not always the same likes and dislikes.

The case is interesting, because it shows that nauseous fluids sometimes occur sporadically, and may thus be intensified by natural selection when required for the purpose of protection.