antis which happened to come a
little nearer the white ants in hue or shape would thereby be enabled to
make a more secure meal upon his unfortunate victims; and so the very
vigilance which the ants exerted against his vile deception would itself
react in time against their own kind, by leaving only the most ruthless
and indistinguishable of their foes to become the parents of future
generations of mantises.

Once more, the beetles and flies of Central America must have learned by
experience to get out of the way of the nimble Central American lizards
with great agility, cunning, and alertness. But green lizards are less
easy to notice beforehand than brown or red ones; and so the lizards of
tropical countries are almost always bright green, with complementary
shades of yellow, grey, and purple, just to fit them in with the foliage
they lurk among. Everybody who has ever hunted the green tree-toads on
the leaves of waterside plants on the Riviera must know how difficult it
is to discriminate these brilliant leaf-coloured creatures from the
almost identical background on which they rest. Now, just in proportion
as the beetles and flies grow still more cautious, even the green
lizards themselves fail to pick up a satisfactory livelihood; and so at
last we get that most remarkable Nicaraguan form, decked all round with
leaf-like expansions, and looking so like the foliage on which it rests
that no beetle on earth can possibly detect it. The more cunning you get
your detectives, the more cunning do the thieves become to outwit them.

Look, again, at the curious life-history of the flies which dwell as
unbidden guests or social parasites in the nests and hives of wild
honey-bees. These burglarious flies are belted and bearded in the very
self-same pattern as the bumble-bees themselves; but their larvae live
upon the young grubs of the hive, and repay the unconscious hospitality
of the busy workers by devouring the future hope of their unwilling
hosts. Obviously, any fly which entered a bee-hive could only escape
detection and extermination at the hands (or stings) of its outraged
inhabitants, provided it so far resembled the real householders as to be
mistaken at a first glance by the invaded community for one of its own
numerous members. Thus any fly which showed the slightest superficial
resemblance to a bee might at first be enabled to rob honey for a time
with comparative impunity, and to lay its eggs among the cells of