Pennant[18] draws attention to the harm the black rat causes by gnawing and devouring not only edibles, but paper, cloth, water-pipes, and even furniture. In England it makes a lodge—either for the day’s residence or a nest for its young—near a chimney, and ‘improves the warmth by forming in it a magazine of wool, bits of cloth, hay, or straw.’ In the East it nests in the indescribable rubbish and ‘unconsidered trifles’ the natives accumulate in their rooms, and is seldom, if ever, interfered with.
Its climbing-habits enable it to ascend trees, and in India it frequently nests among the branches. In some tropical islands M. rattus lives exclusively in the crowns of coco-nut palms, feeding almost entirely on their fruit.
Contrary to the opinion of Blandford, Oldfield Thomas thinks that the black rat originally came from India, and thence spread all over the world, exterminating the indigenous rats of other countries, only to be exterminated later by the arrival of the stronger M. decumanus. At the present time the last-named species is not yet established in some countries—for instance, in those of western South America. On that continent, M. alexandrinus, a tropical variety of M. rattus, is waging war on the less highly organised native rice-rats (Sigmodon). M. alexandrinus has a grey or rufous back, and a white belly.
M. rattus has a milder, more amenable, and tameable character than M. decumanus, and the white, or pied varieties, so dear to schoolboys, are of this species. It is cleanly in its habits, and the skin is kept in excellent order. Like other rats, it holds its food in its hands whilst eating, and it drinks by lapping.
Although the black rat is tending to be driven out by the brown rat, it still lingers on in some warehouses in London, at Yarmouth, in Sutherlandshire, I believe in Lundy Island, and I have been told it occurred not so very long ago on the island in the Serpentine. It doubtless occurs in many other places.
Mus decumanus, the so-called brown rat, undoubtedly comes from Central Asia; and at the present time there is a rat in China described under the name M. humiliatus, which is so little distinguishable from the brown rat that it is thought to be the parent form.
The migration westward of the brown rat certainly took place much later than that of M. rattus. Its first appearance is difficult to date. Undoubtedly large hordes of them crossed the Volga in the year 1727, and continued their journey towards Central Europe. The following year, according to Pennant, brown rats, appeared in England—Jenyns says not till 1730—and almost certainly they came in ships, for on its journey overland it only reached Paris about the year 1750. Reaching England about the year of the second George’s accession, and but thirteen years after the first of the House of Hanover succeeded to the throne, it was called—probably by the adherents of the Stuart cause—the Hanoverian rat. It was also called the Norwegian rat—possibly from the mistaken idea that it reached these islands from that country. It has now passed to the northern half of the New World, where it is gradually driving out many of its weaker brethren. Its numbers are, however, kept within certain limits by wolves, lynxes, raccoons, coyotes, opossums, and other carnivora, and especially by the skunks, which enter barns and out-houses in search of it.
Until the discovery of America, the rat and mouse were unknown in the New World, and the first rats who ever saw it are said to have been introduced in a ship from Antwerp.[19]
The brown rat is of a greyish-brown colour, tinged with yellow and white beneath. The tail is not so long as the body. It is a larger rat than M. rattus, has shorter ears, a more powerful skull, and ten to twelve mammae. Its ears, feet, and tail are flesh-coloured. Like M. rattus, colour varieties occur often: the melanistic variety, not uncommon in Ireland, being sometimes mistaken for the black rat. It is a larger animal than its congener, more heavily built, with a more powerful head, and blunter jaws. The head and body measure some eight to nine inches, but the tail, as a rule, does not surpass the length of the body alone. Its weight averages about nine ounces. It is extremely fierce and extremely cunning, and in the struggle for existence with allied species has hitherto been consistently successful in the fight.
Mus decumanus is very prolific, and produces several litters a year, each averaging eight to ten in number, but twelve or even fourteen young are not very uncommonly born at one time. It begins breeding young—a half-grown female producing a litter of three or four; but in Bombay the sexes do not breed until they have attained at least a weight of 100 grammes. The young are naked, i.e. without hairs, and of a beautiful pink colour. They are blind, and their ears are gummed down over the auditory meatus. They are very weak and helpless, and need that maternal care, which, to do the female rat justice, is never withheld.