There is a melanic or black form of the Brown Rat which is frequently mistaken for the true Black Rat, though the more bulky build and blunter muzzle should show the difference at sight. First recorded from Ireland in 1837, it was considered a distinct species under the name of the Irish Rat. Its fur is uniformly dusky above and below, and the skin is of similar hue. The variation is now known not to be confined to Ireland, but to occur in many parts of England and in the Outer Hebrides. White, fawn-coloured, and pied variations also occur.
The versatility of the Brown Rat is such that it would be idle to attempt any description of its habits. Every one knows at least some part of the story, and the whole of it would require a book. It is the most powerful natural enemy that civilised man has had to contend with, for it attacks him in his own strongholds, spoiling and wasting his food stores and destroying his property in general. There was a time when it could be looked upon more as a commensal because of the valuable scavenging work it performed; but since man has learned that it is safer to attend to this work himself the Rat has become a mere parasitical nuisance. Sir J. Crichton-Browne has estimated the annual loss to this country through the depredations of Rats at £15,000,000 (pre-war figures, 1908).
The Rat is so thoroughly omnivorous that it would be equally absurd to attempt a list of its food: there is nothing that can be eaten that the Rat will not eat. Therefore, there is no possibility of starving him out. Rat-killing campaigns that do not cover every square yard of the country can only have the effect of temporarily mitigating the nuisance; for the Rats' fertility is so great and so rapid that the loss of nine-tenths of a generation is quickly made good. A continental statistician has worked out the theoretical progeny of a single pair of Rats after ten years as reaching the appalling figure of 48,319,698,843,030,344,720! Of course, there is no great value in such a calculation, for it proceeds upon the assumption that every individual lives to become a parent, whereas in fact the mortality in all creatures of such fecundity is enormous, and there are few if any more survivors this year than there were last year. In other words, the great fertility of a race only suffices to make up the wastage from enemy attacks. But the figures serve to show what might happen if the natural control by Weasels, Stoats, Hawks, and Owls were suspended for a short time. But Rats are disseminators of bubonic plague with the aid of their special species of flea.
Water Vole (Arvicola amphibius, Linn.).
In certain directions it appears that failure is the lot of those who have spent the greater part of their lives in trying to spread enlightened views as to the true nature of our native animals and plants. Among a number of such failures two or three may be briefly cited here: you cannot persuade a countryman that a slow-worm is not a snake, that all snakes are not poisonous and to be killed at sight, and that the comparatively inoffensive rodent now to be described is not a rat and of rat-like nature. The name of Water Rat is general as a true folk-name.
The Voles are of heavier build than the Rats, the head is shorter, thicker, and the muzzle rounded instead of being pointed; the limbs are shorter and the hairy tail is not much more than half the length of the head and body. The eyes are small and short-sighted, and the small round ears scarcely project from the surrounding fur, though when listening intently the Vole erects them and makes them more conspicuous. Linnæus, following Ray, described the Water Vole as having webbed feet, but this is incorrect, though the toes of the hinder foot are connected at their base. They are naked and pale pink beneath, with five rounded pads, but above are clothed in stiff hairs. The thick, long, glossy fur is of a warm reddish-brown above, sprinkled with grey, and on the under parts yellowish-grey. This applies chiefly to the male; the female is slightly smaller than her mate, is less bright and more greyish-brown in her coloration. The average length of head and body is seven and a half inches, and of the tapering, ringed tail about four and a half inches. It sometimes occurs with black fur, especially in East Anglia and Scotland; and these examples are usually reported as the Black Rat. Some modern authorities recognise it as a sub-species (reta).
[Pl. 66.]][H 102.
Water Voles fighting.
Arvicola amphibius.