168 NORTH AMERICAN FAUNA [No. 55 



warehouses. Apparently they have not yet penetrated the more arid 

 parts of eastern Oregon. 



General habits. Wharf rats usually enter a new region on ves- 

 sels or railway trains and then spread rapidly from place to place, 

 concealed in boxes, crates, or household goods on trains or freight 

 wagons, or for short distances on foot. They are secretive animals, 

 keeping much under cover or in burrows that they dig in banks 

 or under buildings, rocks, or logs. From one stronghold to an- 

 other they make short trips in the open, mainly at night, although 

 they are often active in the daytime as well as in the dark. They 

 seem to prefer the filth of stables, manure heaps, garbage, and 

 trash piles where they can burrow and revel in dirt and decaying 

 food. They swim well and haunt the wharves and sewer pipes, 

 traveling thence into markets, cellars, and pantries if these are not 

 ratproofed with concrete, brick, stone, or metal. 



Breeding habits. Rats are prolific breeders, having usually 6 

 or 8, but occasionally as many as 15 or 20, young to a litter. The 

 mammae of the adult females are normally 12, 3 pairs of inguinal 

 and 3 pairs of pectoral on 4 distinct mammary glands, 3 mammae 

 on each elongated gland. The period of gestation is 21 days, and 

 many litters are produced throughout the year if sufficient food 

 and shelter are available. 



Foods habits. Scarcely a food or food product can be mentioned 

 that rats will not eat and many nonedible materials are cut, gnawed, 

 and injured in efforts to get at food stores or in burrowing or mak- 

 ing nests. They are filthy and wasteful and often destroy far more 

 than they can eat. They kill and eat chickens or^any young ani- 

 mals they can get, and even gnaw the feet of and injure many kinds 

 of livestock. 



Economic status. Bats have been called the most destructive of 

 all animal pests, not only destroying more food and property than 

 any other animal, but being responsible for the death of more 

 human beings than all the wars of history. They are the hosts of 

 fleas, ticks, and other parasites that convey the germs of disease, 

 including bubonic plague and other fatal maladies. Science and 

 education are waging relentless warfare on the rat and many bulle- 

 tins and circulars have been published giving specific directions 

 for their control and destruction. 



RATTUS RATTUS RATTUS (LINNAEUS) 

 BLACK RAT 



[Mus] rattus Linnaeus, Syst. Nat. ed. 10, v. 1, p. 61, 1758. 



Type locality. Upsala, Sweden. 



General characters. Somewhat smaller than the common rat, slenderer; tail 

 much longer than head and body, slender and nearly naked; ears large and 

 naked; soles naked; pelage in adults coarse and harsh, with long spinescent 

 hairs. Color, black, plumbeous, or sooty, usually plumbeous over lower parts; 

 tail, ears, and feet sooty. Young usually plumbeous all over. 



Measurements. Adult male: Total length, 390 mm; tail, 216; foot, 38; ear 

 (dry), 20, from crown, 15. 



Distribution and habitat. The black rat was brought to North 

 America from Europe in ships at an early date and became abundant 

 before the brown rat was introduced, but it has largely disappeared 



