THE FOOD RELATIONS OF THE CARABIDiE AND 

 COCCINELLIDi:. 



By S. a. FORBES. 



A group or association of animals or plants is like a single 

 organism in the fact that it brings to bear upon the outer world 

 only the surplus of forces remaining after all conflicts interior to 

 itself have been adjusted. Whatever expenditure of energy is 

 necessary to maintain the existing internal balance amounts to so 

 much power locked up, and rendered unavailable for external use. 

 In many groups this latent energy is so considerable and is liable 

 to such fluctuations, that a knowledge of its amount and kinds, 

 and of the laws governing its distribution, is extremely important 

 to one interested in measuring or foreseeing the sum and charac- 

 ter of the outward-tending activities of the class. 



This seems especially true of the insect world. If the checks 

 upon the multiplication of insects and upon their average length 

 of life which are due to insects themselves were to be suddenly 

 removed, there is much reason to suppose that the total external 

 effect of the class would be very greatly intensified, at least for a 

 time. 



Whether our purpose be merely to understand the internal 

 economy of insect life as a part of the general svstem of nature, 

 or to apply such knowledge to a regulation of the depredations 

 of insects upon plants and animals, it is equally necessary that we 

 should know the character and extent of the conflicts which pre- 

 vail within the class, and should understand how the various sub- 

 ordinate groups limit each other's numbers and activity, either 

 indirectly by competition, or directly by destruction. 



The following notes are a contribution to a more exact knowl- 

 edge of this subject than has hitherto prevailed. The view of 

 the functions of the two principal predaceous families of Coleop- 

 tera (Carabidae and Coccinellidse) which is common among 



