144 evolution: the ages and tomorrow 



process; moreover, the various castes are as diverse in behav- 

 ior as they are in structure. In short, there is a completely 

 instinctive, inborn division of labor. 



In Chapter 7, something of the life cycle of these social 

 insects was briefly outlined; but the over-all capacity of 

 their instincts is of further interest, especially the manner 

 in which these instincts organize and unify economic and 

 social life. There is no education or training among ants, in 

 spite of the fact that the individual's social duties require 

 considerable skill. Once the shroud-lilie covering of their 

 pupal stage is removed by their nurses and they have flexed 

 their unused muscles, they are automatically ready for their 

 life's work. Each is equipped with the tools and the instincts 

 to do a thoroughly competent job of nest-building, nursing, 

 tending domesticated stock, fighting, and food-gathering. 

 In the social insects, economic life is based entirely on the 

 direct exchange of food. Ants exchange the contents of 

 their crops, one ant soliciting another by a gentle stroking 

 with its antennae. The liquid is pumped up through the gullet 

 from what Forel called the "social stomach," a common 

 storehouse open to any who may need the contents. Harm- 

 less dyes introduced into the food of ants and griven to a few 

 individuals can be easily seen through the thin skin of the 

 "social stomach" and can be followed through the com- 

 munity as one ant shares its food with another. In a few days 

 traces of the dye will have spread throughout the whole 

 commonwealth. Ants apparently have a well-developed 

 sense of taste and, it would seem, enjoy very much this mul- 

 tiple interchange of food. 



Food-getting in ants is generally a sort of foraging for 

 any bits of food (living or dead) that they can find; but 

 there are also specialized types that carry on an economy 

 based upon domestication of plants or animals, the only in- 

 stance other than man where this occurs. iVorricultural ants 

 have special workers which climb trees and cut out bits of 

 leaves. The leaf bits are held aloft over the rather large 



