Bates satisfactorily answers this question by
showing that the form which is imitated keeps the usual dress of the group
to which it belongs, while the counterfeiters have changed their dress and
do not resemble their nearest allies.
We are next led to enquire what reason can be assigned for certain
butterflies and moths so often assuming the dress of another and quite
distinct form; why, to the perplexity of naturalists, has nature
condescended to the tricks of the stage? Mr. Bates has, no doubt, hit on
the true explanation. The mocked forms, which always abound in numbers,
must habitually escape destruction to a large extent, otherwise they could
not exist in such swarms; and a large amount of evidence has now been
collected, showing that they are distasteful to birds and other insect-
devouring animals. The mocking forms, on the other hand, that inhabit the
same district, are comparatively rare, and belong to rare groups; hence,
they must suffer habitually from some danger, for otherwise, from the
number of eggs laid by all butterflies, they would in three or four
generations swarm over the whole country. Now if a member of one of these
persecuted and rare groups were to assume a dress so like that of a well-
protected species that it continually deceived the practised eyes of an
entomologist, it would often deceive predaceous birds and insects, and thus
often escape destruction.
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