THEIR RELATION TO EACH OTHER 125 



parasites, checking in turn too great a reduction among 

 the primaries. 



It is a merry war in which all these organisms are 

 engaged, each one aiming only at food for itself and 

 its progeny, and yet each playing its part in that game 

 of life in which man seems to be the only one capable 

 of appreciating the conditions, though he is himself 

 involved and a sufferer as well as a factor in the game. 



It is a pleasure to be able to say that the relation 

 of active hostility is not the only one existing between 

 insects. Between some there is at least toleration; 

 as between others an active friendship based on mutual 

 advantage; in a few cases there is almost absolute 

 dependence. 



The first case of this kind that comes to mind is the 

 relation of certain ants to certain plant lice, and assuredly 

 we have nothing in the range of insect behavior that 

 exceeds in interest this cultivation or fostering of a 

 creature so far different, until we get it in the relation 

 of the human being to his domestic animals. The 

 relation is even closer, because so much has the lapse 

 of time acted upon this interdependence that, while 

 the elimination of the plant louse might make little 

 difference to the ant, the elimination of the ant would, 

 in many cases, mean the destruction of the plant louse. 



It is not possible in this connection to do more than 

 mention the fact that among the social insects there 

 are a number of different castes and forms, each of which 

 has its own function in the community. That is a mat- 

 ter of internal administration and is regulated by each 

 species in accordance with the conditions which have 

 been developed by the stress of the surroundings. It 

 is a little different when the matter of slavery comes 

 to be considered; when we find that certain species 

 of ants actually make war upon weaker forms to obtain 



