Rats probably exceed any other variety of mammal in the number of individuals, and their fecundity and secretive habits add greatly to the difficulties of the rat problem. Under normal conditions a female rat will bear three to five litters of ten each year. At this rate, one pair of rats would in five years increase to over nine hundred billion, provided all survived. The number of rats in any given place is limited only by the amount of available food and the facilities to nest.
The economic losses from rat depredation in the United States alone are estimated to vary from thirty-five to fifty million dollars a year. They consist mostly in damage to grain, merchandise, poultry, eggs and other foodstuffs. Rats also set fire to buildings, destroy furniture, gnaw lead pipes, weaken embankments, undermine foundations, piers, etc. So far as anyone has been able to make out, rats