It is only in external matters, however, that the appearance of such
mimetic species can ever be altered. Their underlying points of
structure and formative detail always show to the very end (if only one
happens to observe them) their proper place in a scientific
classification. For instance, these same parasitic flies which so
closely resemble bees in their shape and colour have only one pair of
wings apiece, like all the rest of the fly order, while the bees of
course have the full complement of two pairs, an upper and an under,
possessed by them in common with all other well-conducted members of the
hymenopterous family. So, too, there is a certain curious American
insect, belonging to the very unsavoury tribe which supplies London
lodging-houses with one of their most familiar entomological specimens;
and this cleverly disguised little creature is banded and striped in
every part exactly like a local hornet, for whom it evidently wishes
itself to be mistaken. If you were travelling in the wilder parts of
Colorado you would find a close resemblance to Buffalo Bill was no mean
personal protection. Hornets, in fact, are insects to which birds and
other insectivorous animals prefer to give a very wide berth, and the
reason why they should be imitated by a defenceless beetle must be
obvious to the intelligent student. But while the vibrating wing-cases
of this deceptive masquerader are made to look as thin and hornet-like
as possible, in all underlying points of structure any competent
naturalist would see at once that the creature must really be classed
among the noisome Hemiptera.
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