nS ANTS. 



u>e not only pervades the activities of the adult worker but extends 

 even to the more inert larval stages. Thus the latter represent a rich 

 and ever-fresh supply of food that can be devoured whenever a tem- 

 porary famine overtakes the colony. In certain species, like the East 

 Indian CEcoplivlla smaragdina and the South American Camponotns 

 scitc.r, the larvae are more humanely employed as spinning machines 

 for constructing the silken nest inhabited by the colony (see p. 216). 

 These examples also illustrate the purposive manner in which an 

 organism can satisfy definite needs by taking advantage of ever- 

 present opportunities. 



In the lives of the social insects the threptic, or philoprogenitive 

 instincts are of such transcendent importance that all the other instincts 

 of the species, including, of course, those of alimentation and nest- 

 building, become merely tributary or ancillary. In ants, especially, 

 the instincts relating to the nurture of the young bear the aspect of a 

 dominating obsession. Their very strength and scope render the 

 insects more susceptible to the inroads of a host of guests, commensals 

 and parasites. Besides the parasitic larvae of Chalcidids, Lomechusini 

 and Mctopina, to be described in Chapter XXII, there are many adult 

 beetles and other insects on which the ants lavish as much attention as 

 they do on their own brood. And when the ants themselves become 

 parasitic on other ants, it is always either for the sake of having their 

 <>wn brood nurtured, as in the temporarily and permanently parasitic 

 forms, or for the purpose of securing the brood of another species, as 

 in the slave-making species. 



The philoprogenitive instincts arose and were highly developed 

 among the solitary ancestral insects long before social life made its 

 appearance. In fact, social life is itself merely an extension of these 

 instincts to the adult offspring, and there can be no doubt that once 

 developed it reacted rapidly and powerfully in perfecting these same 

 instincts. It is not so much the fact that all these activities of the 

 social insects converge towards and center in the reproduction of the 

 species, for this is the case with all organisms, as the elaborate living 

 environment developed for the nurture of the young, that gives these 

 insects their unique position among the lower animals. A full analysis 

 of the threptic instincts would involve a study of the entire ethology 

 of the social insects and cannot be undertaken at the present time. 

 Nevertheless the bearing of these activities on the subject of poly- 

 morphism can hardly be overestimated and deserves to be emphasized 

 jn this connection. 



All writers agree in ascribing polymorphism to a physiological 

 division of labor among originally similar organisms. This is tanta- 



