146 evolution: the ages and tomorrow 



repletes. These repletes have so modified and enlarged their 

 gullet or crop that it can be swelled to the size of a pea. At 

 the end of the wet season the repletes hang themselves from 

 the ceiling of the underground cellars, and the workers pro- 

 ceed to fill them full of the aphid honey dew. For months 

 afterward the repletes can be tapped by any worker, and 

 the colony is kept alive through what would otherwise be 

 a season of famine. 



Among the ants there are many variations on this theme 

 of molding the structure of the individual so that it becomes 

 a tool of the whole community; even the young grubs are 

 sometimes modified and used for work in the common cause 

 in a sort of child labor. Ants have also exploited other ani- 

 mals in a close parallel to man's domestication of cattle be- 

 cause they can transform inedible grass into milk and meat. 

 Ants have no sucking mouth parts, only biting, and hence 

 they are unable to get at the rich nutritive saps of the plant 

 world about them. Aphids and coccids, which normally feed 

 on plant juices, are domesticated by some species of ants. 

 Both these insects are wasteful in their feeding;- and do not 

 digest all the hquids they take from plants; some of it 

 oozes out in the form of sweet droplets. It is this character- 

 istic, particularly in the aphids, which is so highly exploited 

 by ants. Some species of ants are content to merely lick up 

 the sweetened drops which are deposited around feeding 

 aphids; other species catch the drops as they ooze from the 

 sap-eater's body; and still other ants actually "milk their 

 cows" by caressing them with their antennae. The last are 

 the most specialized. Some excavate underground rooms 

 around roots and set their cows out to pasture. Ants even 

 tend the aphid eggs through cold weather and set them out 

 on plants to hatch in the spring. Just as man does, some build 

 little wood-pulp stables for their cows, not in the main ant 

 house, but off to the side connected by a covered passage. 

 iVnts have also closely paralleled man's enslavement of man, 

 even to organized ant raids to capture ant slaves. And some 



