Happily, however, the tyrants and murderers do not always have things
all their own way. Sometimes the inoffensive prey turn the tables upon
their torturers with distinguished success. For example, Mr. Wallace
noticed a kind of sand-wasp, in Borneo, much given to devouring
crickets; but there was one species of cricket which exactly reproduced
the features of the sand-wasps, and mixed among them on equal terms
without fear of detection. Mr. Belt saw a green leaf-like locust in
Nicaragua, overrun by foraging ants in search of meat for dinner, but
remaining perfectly motionless all the time, and evidently mistaken by
the hungry foragers for a real piece of the foliage it mimicked. So
thoroughly did this innocent locust understand the necessity for
remaining still, and pretending to be a leaf under all advances, that
even when Mr. Belt took it up in his hands it never budged an inch, but
strenuously preserved its rigid leaf-like attitude. As other insects
'sham dead,' this ingenious creature shammed vegetable.
In order to understand how cases like these begin to arise, we must
remember that first of all they start of necessity from very slight and
indefinite resemblances, which succeed as it were by accident in
occasionally eluding the vigilance of enemies. Thus, there are stick
insects which only look like long round cylinders, not obviously
stick-shaped, but rudely resembling a bit of wood in outline only. These
imperfectly mimetic insects may often obtain a casual immunity from
attack by being mistaken for a twig by birds or lizards.
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