Fig. 46.—Mus decumanus. (From Pennant.)
M. decumanus is less attached to the dwellings of man than M. rattus; still, it does live in houses, though, owing to a lack of climbing power, it is never found above the third floor. It is largely a burrowing animal, and makes its nests in its burrows. M. rattus can also burrow, but not so readily, and it nests not in the burrow, but in some obscure corner. A curious instance of the nesting habits of this species was found during the rebuilding of my ‘lodgings’ in 1911. In searching under the boards of the floor of the rooms of our Foundress the Lady Margaret, Mother of Henry VII, now the drawing-room, the workmen found the mummified remains of four rats, which had taken to themselves coverings or shrouds; and upon investigation these proved to consist of a vellum deed relating to the College, some paper documents relating to Thomas Thompson, who was Master of the College from 1510 to 1517, and some fragments of printed matter which turned out to be part of an early Virgil; four leaves of a Horace; two leaves of a primer of Wynkyn de Worde; and finally a leaf of a work by Caxton. In addition, four playing-cards of the sixteenth century were found.
The brown rat frequents barns, granaries, stables, slaughter-houses, rivers, ponds, ditches, drains, gullies, and sewers—it is, in fact, sometimes called the sewer-rat. It is less particular in its food than the black rat, which is more usually found in grain-stores. Although in Bombay the relative numbers of M. rattus and M. decumanus caught was as seven is to three, in open spaces, gardens, &c., the latter was much the commoner. Yet the report of the Plague Commission states that the authors ‘do not think it an exaggeration to state that every inhabited building in Bombay City and Island, not excepting even the better-class bungalows, shelters its colony of M. rattus.’
Fig. 47.—Head of Mus decumanus. (From Flower and Lyddeker.)
Both species readily take to water, though M. rattus, being the better climber, more readily gets on shipboard. They will swim rivers and arms of the sea. The rats which infest the London Zoological Gardens are said to swim nightly the canal in Regent’s Park. Rats constantly make their way to coastal islands, and in a comparative short time clear the place of indigenous rabbits and birds. Puffin Island, off the coast of Anglesea, and the Copeland Islands, in Belfast Bay, are two examples of islands at one time leased for the sake of their rabbits to people who had to give up the lease after the rats had landed on them. Similar cases are known off Denmark. They greedily eat birds’ eggs, and are said to convey them over considerable distances, though how they do this is not very clear. After the destruction of the vertebrate land-fauna, they fall back upon the dwellers in the littoral, and live on prawns, shrimps, and molluscs. They are very fond of fish, and Lyddeker, in the ‘Royal Natural History,’ states that they occasionally catch and eat young eels. As their parasites show, they eat insects such as the meal-beetle, and when in the field they eat land-snails, insect larvae, and other food, which conveys into their bodies the same tape-worms, &c., which we find in the hedgehog and in the smaller carnivora.
They are, in fact, omnivorous, and nothing in the way of human food is alien to them. They do enormous harm to corn-ricks and to stored grain. They are inveterate enemies of the hen-roost, the pigeon-house, and, as we have seen, of the rabbit-warren. When pressed by hunger, they readily turn cannibal, and the brown rat easily masters the black. There are stories of some few specimens of each species being left in a cage overnight; on the following morning there were only brown rats in that cage. To some extent they help to keep down one of the field-mice (Genus Microtus), and this is especially the case in North America;[20] but the benefit is doubtful since they are held to be at least as destructive to the crops as the field-mice, and probably more so.
The ferocity with which they defend themselves when attacked is well known, and at times, when they are driven by hunger, they do not hesitate to attack man. They are said to nibble the extremities of infants, and in one—apparently authentic—instance they overcame and devoured a man who had entered a disused coal-mine tenanted by starving rats. The bite is said to be severe (they will bite through a man’s thumb-nail into the flesh), and the bite is long in healing.
Rats eat much garbage and offal, and readily feed upon dead bodies. About sixty years ago there stood, at Monfaucon, a slaughter-house for horses, and this it was proposed to remove still farther from Paris. It is stated that the carcasses of the horses slaughtered—which sometimes amounted to thirty-five a day—were cleared to the bone by rats in the course of the following night. This excited the attention of a M. Dusaussois, who made the following experiment: He placed the carcasses of two or three horses in an enclosure, which permitted the entrance of rats by certain known and closable paths. Towards midnight, he and some workmen entered the enclosure, closed the rat-holes, and in the course of that night killed 2650 rats. He repeated the experiment, and by the end of four days had killed 9101 rats, and by the end of a month 16,050 rats. During the process of these experiments other carcasses were exposed in the neighbourhood, so that in all probability M. Dusaussois attracted to his enclosure but a small proportion of the total available number of rats. All around this slaughter-house the country was riddled with extensive burrows, so that the earth was constantly falling in. In one place the rodents had formed a pathway, 500 yards long, leading to a distant burrow.