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.
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 rôles in conveying other diseases to human beings. They are parasites, without redeeming characteristics, and should everywhere be routed and destroyed.
PROTECTION OF FOOD AND OTHER STORES FROM RATS AND MICE.
Past attempts to exterminate rats and mice have failed, not so much because of lack of effective means as because of the neglect of necessary precautions and the absence of concerted endeavors. We have rendered our work abortive by continuing to provide subsistence and hiding places for the animals. If these advantages are denied, persistent and general use of the usual methods of destruction will prove far more successful.