404 ELEMENTARY ZOOLOGY. 



and something to control them. The most effective 

 means thus far found is by spraying plants, to keep away 

 the females when about to lay, or to kill the young; the 

 rotation of the. crops in such a way that the insects may 

 hatch without finding the kind of food on which they 

 depend ; and the introduction of animals, either predatory 

 or parasitic, that attack the hurtful species. 



Occasionally through a period of years such animals 

 will multiply to such an extent as to become a plague, 

 when in ordinary years they merely reduce the returns 

 of the agriculturalist. Such are the outbreaks of the 

 Rocky Mountain locust, the Hessian fly, the San Jose 

 scale, the chinch bug, and the like. Less frequently 

 similar things happen in respect to other animals, as the 

 plague of rabbits in Australia, and of the rats in the 

 Bermudas. 



405. Domestication of Animals. Occasional reference 

 has been made in the preceding paragraphs to the 

 domestic animals. This means something quite different 

 from the merely useful animals. This term refers to 

 the control by man of the life and habits of animals to 

 such degree that he can work his will with them almost 

 irrespective of the natural conditions. This domestica- 

 tion began before man emerge^ from the savage state 

 before recorded hjstory began. The dog and cat were 

 doubtless among the earliest forms, and the camel, the 

 horse, the sheep, the donkey, the hog, the pigeon, the 

 chicken, all have been very long in domestication. 



The qualities that would make an animal suitable for 

 domestication, and which doubtless helped to determine 

 what forms should be domesticated, are : some gentleness 

 of temper and lack of extreme nervousness, capability 



