Losses from depredations of house rats amount to many millions of
dollars yearly--to more, in fact, than those from all other injurious
mammals combined. The common house mouse[1] and the brown rat[2] (fig.
1), too familiar to need description, are pests in nearly all parts of
the country; while two other kinds of house rats, known as the black
rat[3] and the roof rat,[4] are found within our borders.
[Illustration: FIG. 1.--Brown rat.]
Of these four introduced species--for none is native to America--the
brown rat is the most destructive, and, except the mouse, the most
numerous and most widely distributed. Brought to America just before
the Revolution, it has supplanted and nearly exterminated its less
robust relative the black rat; and in spite of the constant warfare of
man has extended its range and steadily increased in numbers. Its
dominance is due to its great fecundity and its ability to adapt itself
to all sorts of surroundings. It breeds (in the middle part of the
United States) six or more times a year and produces from 6 to 20 young
(average 10) in a litter. Females breed when only 3 or 4 months old.
Thus a pair, breeding uninterruptedly and without deaths, could in three
years (18 generations) produce a posterity of 359,709,480 individuals.
Mice and the black and roof rats produce smaller litters, but the period
of gestation, about 21 days, and the number of litters are the same for
all.
Rats and mice are practically omnivorous, feeding upon all kinds of
animal and vegetable matter. The brown rat makes its home in the open
field, the hedge row, and the river bank, as well as in stone walls,
piers, and all kinds of buildings. It destroys grains when newly
planted, while growing, and in the shock, stack, mow, crib, granary,
mill, elevator, or ship's hold, and also in the bin and feed trough. It
invades store and warehouse and destroys furs, laces, silks, carpets,
leather goods, and groceries. It attacks fruits, vegetables, and meats
in the markets, and destroys by pollution ten times as much as it
actually eats. It destroys eggs and young poultry, and eats the eggs and
young of song and game birds. It carries disease germs from house to
house and bubonic plague from city to city. It causes disastrous
conflagrations; floods houses by gnawing lead water pipes; ruins
artificial ponds and embankments by burrowing; and damages foundations,
floors, doors, and furnishings of dwellings.
Unlike the brown rat the black rat rarely migrates to the fields. It has
disappeared from most parts of the Northern States, but is occasionally
found in remote villages or farms. At our seaports it frequently arrives
on ships from abroad, but seldom becomes very numerous. The roof rat is
common in many parts of the South, where it is a persistent pest in cane
and rice fields. It maintains itself against the brown rat partly
because of its habit of living in trees. The common house mouse by no
means confines its activities to the inside of buildings, but is often
found in open fields, where its depredations in shock and stack are well
known.
Not only are mice and rats, especially the brown rat, a cause of
destruction and damage to property, but they are also a constant menace
to the health of man. It has been proved that they are the chief means
of perpetuating and transmitting bubonic plague and that they play
important roles in conveying other diseases to human beings. They are
parasites, without redeeming characteristics, and should everywhere be
routed and destroyed.