Again, the supposed war of
extermination waged in Europe by the brown rat against the black rat is
(as Chalmers Mitchell points out) pure fiction. In England, where this
war is said to have been ferociously waged, both rats exist and
flourish, and under conditions which do not usually even bring them into
competition with each other. The black rat (_Mus rattus_) is smaller
than the other, but more active and a better climber; he is the rat of
the barn and the granary. The brown or Norway rat (_Mus decumanus_) is
larger but less active, a burrower rather than a climber, and though
both rats are omnivorous the brown rat is more especially a scavenger;
he is the rat of sewers and drains. The black rat came to Northern
Europe first--both of them probably being Asiatic animals--and has no
doubt been to some extent replaced by the brown rat, who has been
specially favoured by the modern extension of drains and sewers, which
exactly suit his peculiar tastes. But each flourishes in his own
environment; neither of them is adapted to the other's environment;
there is no war between them, nor any occasion for war, for they do not
really come into competition with each other. The cockroaches, or
"blackbeetles," furnish another example. These pests are comparatively
modern and their great migrations in recent times are largely due to
the activity of human commerce. There are three main species of
cockroach--the Oriental, the American, and the German (or Croton
bug)--and they flourish near together in many countries, though not with
equal success, for while in England the Oriental is most prosperous, in
America the German cockroach is most abundant.
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