8 



Rats and Mice 



of its more salubrious station, it is a far cleaner feeder than 

 B. 7iorvegicus. 



B. norvegicus is essentially a water loving and burrowing 

 animal ; although far less agile than B. rattiis, it is also a good 

 climber. As compared with the last named species, it is far more 

 voracious and cunning ; its greater size and strength, and its 

 much greater fecundity, render it, so far as material prosperity is 

 concerned, a much more formidable enemy of mankind. On the 

 other hand, although it spreads many serious or fatal diseases, it 

 usually exhibits a certain shyness of man, so that, in normal 

 conditions, it is probably slightly less important than B. rattus as 

 a carrier of plague. 



It possesses a remarkable power of adapting itself to the most 

 varied surroundings. Thus, although extremes of heat and cold 

 are unfavourable to its development and continued success, it may 

 be found living in many hot countries and also in cold storage 

 stations. At Tammerfors, a little town of wooden buildings in 

 western Finland, and a very cold place, it has, according to 

 Zuschlag, invaded the houses and completely replaced the House 

 Mouse. Here it has become most impudent and bold ; it is to be 

 found even in the beds of the inhabitants. In such conditions it 

 must constitute a grave menace to the public health. Again, in 

 South Georgia it is regularly found out of doors in the summer, living 

 amongst the coarse tussock grass of that wind- and snow-sw^ept 

 island, and preying upon the eggs and young of the sea-birds. 



The only factor indispensable for the success of this species is 

 the presence of water ; it drinks freely and displays great skill as 

 a swimmer and diver. Naturally, therefore, it abounds along the 

 banks of all watercourses ; and these play a great part in directing 

 and facilitating its advance in a new country, as well as its 

 seasonal movements or " migrations." It infests sewers and 

 drains, not only for the sake of the water flowing through them, 

 but because ordure serves it quite well as food. From such 

 haunts it readily passes into the basements of buildings, and in 

 those houses which have their tanks in the roofs it often finds its 

 way aloft. Where a rat has found such a pleasant and safe 

 drinking and bathing place it will sometimes visit it with the 

 utmost regularity for a considerable period ; if living out of doors, 

 the rat will enter such a house, and leave it again after bathing, 

 night after night, by a regular run, which may include a long 

 climb through a stack pipe and a tortuous passage through walls, 



