Contributions to the theory of natural selection. A series of essays ... By Alfred Russel Wallace ...

78 MIMICRY, AND OTHER PROTECTIVE
birds more easily than almost any other insects, their
great abundance all over the wide region they inhabit
shows that they are not so persecuted. It is to be especially remarked also, that they possess no adaptive
colouring to protect them during repose, for the under
side of their wings presents the same, or at least an
equally conspicuous colouring as the upper side; and
they may be observed after sunset suspended at the end
of twigs and leaves where they have taken up their
station for the night, fully exposed to the attacks of
enemies if they have any. These beautiful insects
possess, however, a strong pungent semi-aromatic or
medicinal odour, which seems to pervade all the juices
of their system. When the entomologist squeezes the
breast of one of them between his fingers to kill it, a
yellow liquid exudes which stains the skin, and the
smell of which can only be got rid of by time and repeated washings. Here we have probably the cause of
their immunity from attack, since there is a great deal
of evidence to show that certain insects are so disgusting to birds that they will under no circumstances
touch them. 3Mr. Stainton has observed that a brood
of young turkeys greedily devoured all the worthless
moths he had amassed in a night's ( sugaring," yet
one after another seized and rejected a single white
moth which happened to be among them. Young pheasants and partridges which eat many kinds of caterpillars seem to have an absolute dread of that of the
common currant moth, which they will never toucl, and
tomtits as well as other small birds appear never to eat