642 THE AMERICAN NATURALIST [Vol. XLIII 



large number of living forms await study from a similar 

 point of view. 



If we determine accurately the work of an individual 

 and multiply this by the number of individuals, we have 

 an expression of the species as a force in nature. Hence 

 it is true, in general, that the commoner or more numer- 

 ous a species is, the more important its biological work. 

 We accordingly begin this series of dynamic studies with 

 one of the commonest of American animals. 



Of the ten species of BufonidaB now recognized in the 

 United States B. I. americanus has the widest range, 

 which includes almost the entire continent of North 

 America east of the Rocky Mountains. It is, therefore, 

 probably the most valuable type of the group. 



The insect problem, further, is one of the most im- 

 portant in the entire field of American natural history. 

 It finds partial expression in the annual tax of $795,100,- 

 000 which insects impose upon our agricultural resources. 

 This is a rigidly conservative estimate made by the 

 department of agriculture and does not include costs of 

 abating annoyance or losses of household goods or those 

 occasioned by spread of human disease. A large pro- 

 portion of this loss might be most economically prevented 

 by a reasonable knowledge and utilization of insectivo- 

 rous animals. With all our books, bulletins and talk about 

 it, we have scarcely made a practical beginning in this 

 direction as a people. 



In seeking animal allies to aid in the solution of the 

 insect problem we should choose those which will do the 

 work required most effectively and at the same time 

 present the fewest objectionable features. A good many 

 birds are efficient destroyers of insects, but become in- 

 jurious if their numbers are unduly increased. Many 

 insects are parasitic and predaceous, but, in general, 

 their breeding or regulation is beyond human control. 

 Clearly an animal to be depended upon to hold insects 

 in check should be one which man can breed in any de- 

 sired numbers and, on account of the enormous repro- 

 ductive possibilities of insects, a form which he can in- 



