18 THE BROWN RAT IN THE UNITED STATES. 



the animals multiply greatly; when this food fails they are forced to 

 the cultivated districts for subsistence. In 1878 almost the entire 

 crops of corn, rice, and mandioca in the State of Parana were destroyed 

 by rats, causing a serious famine. 



An invasion of black rats (Mus rattus) in the Bermuda Islands 

 occurred about the year 1615. In a space of two years they had in- 

 creased so alarmingly that none of the islands were free from them. 

 The rodents devoured everything which came in their way — fruit, 

 plants, and even trees — so that for two years the people were destitute 

 of bread. A law was passed requiring every man in the islands to set 

 12 traps. In spite of all efforts, the animals increased, until they 

 finally disappeared with a suddenness which could have resulted only 

 from a pestilence. 6 



FOOD OF RATS. 



The brown rat is practically omnivorous. The statement applies 

 as well to the black rat and the roof rat. Their bill of fare includes 

 seeds and grains of all kinds, flour, meal, and food products made 

 from them ; fruits and garden vegetables ; mushrooms ; bark of growing 

 trees; bulbs, roots, stems, leaves, and flowers of herbaceous plants; 

 eggs, chicks, ducklings, young pigeons, and young rabbits; milk, butter, 

 and cheese; fresh meat and carrion; mice, rats, fish, frogs, and 

 mussels. This great variety of food explains the ease with which 

 rats adapt themselves to almost every environment. 



Experiments show that the average quantity of grain consumed 

 by a full-grown rat is fully 2 ounces daily. A half-grown rat eats 

 about as much as an adult. Fed on grain, a rat eats 45 to 50 pounds 

 a year, worth about 60 cents if wheat, or $1.80 if oatmeal. Fed on 

 beefsteaks worth 25 cents a pound, or on } r oung chicks or squabs 

 with a much higher prospective value, the cost of maintaining a rat 

 is proportionately increased. Granted that more than half the food 

 of our rats is waste, the average cost of keeping one rat is still upward 

 of 25 cents a year. 



If an accurate census of the rats of the United States were possible, 

 a reasonably correct calculation of the minimum cost of feeding them 

 could be made from the above data. If the number of rats supported 

 by the people throughout the United States were equal to the number 

 of domestic animals on the farms — horses, cattle, sheep, and hogs — 

 the minimum cost of feeding them on grain would be upward of 

 $100,000,000 a year. To some such enormous total every farmer, 

 and indeed every householder who has rats upon his premises, con- 

 tributes a share. 



But, as will be shown later, the actual depredations of rats are by 

 no means confined to what they eat. They destroy fully as much 



a Nature, vol. 20, p. 65, 1879. 



b Popular Science Monthly, vol. 12, p. 376, June, 1878. 



