10 ANIMAL COMPETITORS 
ington the average litter is 10. A pair and 
their progeny breeding three times a year 
would, thus, if all remained alive, produce a 
population of more than 20,000,000. ‘‘Of 
course, such results never occur in nature. 
Apparently not nearly half the rats born are 
females; at least, among mature rats the males 
greatly predominate. Then, too, the life of 
young rats, as well as that of the old, is a con- 
tinuous struggle for existence. Disease, the 
elements, natural enemies, the devices and cun- 
ning of man, and even cannibalism are contin- 
ually at work to reduce their numbers.’’ 
The young are born, after a gestation period 
of 21 days, in a burrow dug in the ground under 
buildings, piles of lumber or wood, beneath 
strawstacks, etc., or simply bored into a stream- 
bank. They are naked and blind at birth, but 
develop with great rapidity. 
What it costs to board our rats. The dam- 
age done by rats over so great an area as 
the United States or Canada, is incalculable. 
David E. Lantz, in the document from which 
I am quoting freely, summarizes their destruc- 
tion thus: 
