204 SCIENCE REMAKING THE WORLD 



exhibit an extraordinary degree of variety and special- 

 ization in economic organization. Some kinds are 

 agriculturalists, and collect and store up seeds, some 

 are hunters and marauders and travel about in large 

 armies, some make slaves of other ants, some care for 

 plant lice and scale-insects, which secrete honey dew 

 a favourite food of the ants not only to the extent of 

 protecting these helpless "ant cattle" from predaceous 

 insect enemies but even to the extent of taking care of 

 their eggs and putting the newly hatched young on 

 proper plants for their nourishment. 



There is a well-known little brown ant common in 

 the cornfields of the Mississippi Valley which collects 

 the eggs of the corn-root plant-louse, laid in the autumn 

 in the soil, carries them into its nests and protects 

 them through the winter. In the spring these plant- 

 louse eggs hatch before the corn has been planted and 

 there are no corn roots yet for the plant-lice to feed on, 

 so the ants place the delicate little plant-louse babies 

 on the roots of an early weed, called pigeon grass, that 

 grows in the cornfields. Then when the corn is planted 

 and the corn roots are developed the ants carry the 

 plant-lice from the pigeon-grass roots to the corn 

 roots. 



Why this interest on the part of the ants in the plant- 

 lice? Because the plant-lice secrete, while they are 

 sucking sap from the corn roots, a plentiful supply of 

 that honey dew which is so favourite a food of the ants. 

 Thus through this interesting social relation between 

 the ants and the plant-lice, these latter get protected 

 and cared for and the former get a welcome supply of 



