X INTRODUCTION 



sions in the distribution of those already affected by a 

 changed environment. A quite considerable part of this 

 motley assemblage consists of insects, which enter into our 

 life and activities in many ways. This group of animals 

 really vies with the mammals, and with man in particular, in 

 its attempt to dominate the animal world. With this end in 

 view, insects have several points in their favor which must 

 not be forgotten at the outset, although they are dealt with 

 at greater length in the succeeding chapters. There are many 

 more dififerent kinds of insects than there are of other animals 

 and it follows from this, if for no other reason than as a mat- 

 ter of chance, that they will cross our path at many places. 

 They are small, extremely tenacious of life and endowed with 

 such great powers for reproduction and multiplication that 

 the abundance of any particular species responds very 

 rapidly to changes in food supply, or other variable factors 

 in their surroundings. Although in great part terrestrial or 

 aquatic during their preparatory stages, they are typically 

 winged and adapted to an aerial life in their mature condition. 

 In addition, some are parasites of various plants, animals, 

 and even in other insects, till it would seem that about every 

 method of earning a living, or of securing it otherwise, may 

 find its counterpart in some insect. Endowed as a natural 

 consequence also with a great fixity of purpose dependent 

 upon their purely instinctive behavior, insects do not respond 

 readily as a class to our efforts to thrust them aside and out 

 of oiu" way. 



What can be more persistent than the well-directed flight 

 of the hungry mosquito in its search for human blood. Much 

 has been learned concerning the hidden dangers that lie in 

 the wake of the mosquito bite, but little has been accom- 

 plished toward banishing the mosquito tribe. Quite properly 

 no biologist has entertained the idea that the instincts of the 

 mosquito or for that matter of any other insect could be 

 altered in the least. The only remedies which can be pro- 

 posed at the present time for dangerous, annoying, or de- 

 structive insects depend upon actually destroj'ing them. 



