CHAPTER XIII
RATS[15] (Mus or Epimys)
Now, Muse, let’s sing of rats!
(Grainger.)
The overwhelming majority of rats fall under two species: (i) Mus rattus, the black rat, and (ii) Mus decumanus, the brown rat. The original home of both species is, according to Dr. Blandford, Mongolia; but the date of their first appearance in our islands is a matter of some uncertainty. According to Helm, M. rattus passed into Europe at the time of the Völkerwanderung, and doubtless accompanied the migrating Asiatic hordes on their journeys westward. The name rat appears in early High-Dutch glossaries, it is mentioned by Albertus Magnus, and occurs in early Anglo-Saxon writings in England. This evidence is, however, not conclusive that in those times the rat had entered Great Britain; indeed, according to Bell,[16] the black rat was not known here until before the middle of the sixteenth century: at least, he says, no author more ancient than that period has described, or even alluded to, it as being in Great Britain, Gesner being the first to do so. Jenyns, in his ‘Manual of British Vertebrate Animals,’[17] describes M. rattus as ‘truly indigenous’; but this is in comparison with the brown rat, whose comparatively recently arrival he chronicles. M. rattus is said to have been common on the continent of Europe in the thirteenth century.
Fig. 44.—Mus rattus. (From Pennant.)
M. rattus has, as a rule, greyish-black fur above, ash-coloured below, with a tail a little longer than the body and head. It is smaller and more elegantly built than the brown rat; its snout is longer and more slender, and the long, thin, scaly tail is about eight or nine inches in length. The British forms average in length seven inches from the tip of the nose to the origin of the tail. Although known as the black rat, its bluish, or greyish-black colour is, both in the East and in Northern America, frequently replaced by brown on the upper surface, and by white fur on the lower, or by a yellowish-brown rufous colour. The ears, feet, and tail are black. When kept as pets—and they frequently are—white and piebald varieties are often bred. The ears are larger in proportion than in M. decumanus, the rings of scales on the tail better marked, and spines in the fur are not uncommon.
The black rat, or Old-English rat, begins to breed under the age of one year, and goes with young six weeks; it breeds frequently during the year, but does not commence in Bombay, according to the Plague Commission, until it has attained the weight of at least 70 grammes. In India they breed all the year round. In Britain they produce six to eleven young at a time; in India the average is 5·2; the largest number found by the Plague Commission having been nine. In Bombay it is noteworthy that in both species the percentage of young rats to the total rat population is greater during the warmer months—from June to October—than at other times of the year. It is also noteworthy that the fall in fertility begins before the onset of the plague epizootic, though, later, it roughly coincides with it. In Britain they increase so fast as to overstock their abode, and thus they are forced, from deficiency of food, to devour one another, and this alone, Pennant thinks, ‘prevents even the human race from becoming a prey to them, not but there are instances of their gnawing the extremities of infants in their sleep.’
Fig. 45.—Head of Mus rattus. (From Flower and Lyddeker.)