INTERDEPENDENCE OF ORGANISMS 



53 



clean the surface. These anxious cares are of course ex- 

 plained by the use the ants make of the root louse [aphid], 

 whose excreted fluids they lap up greedily as soon as the 

 young lice begin to feed. 



'That the young of the first generation are helped by the 

 ants to a favorable position on the roots of the plants they 



infest is quite beyond ques- 

 tion. . . We have repeat- 

 edly performed the experiment 

 of starting colonies of ants on 

 the hills of corn in the in- 

 sectary, and exposing root lice 

 from the field to their attention 

 and in every such instance, if 

 the colony was well established 

 the helpless insects have been 

 seized by the ants, often almost 

 instantly, and conveyed under 

 ground, where we would later 

 find them feeding on the roots 

 of the corn. 



"I need hardly say that the 

 relations above described be- 

 tween the corn-root aphis and 

 these ants continue without 

 cessation throughout the year." 



Thus sequestered from parasites, and guarded by the ants 

 and cared for at every turn, this long unknown aphid has 

 flourished inordinately, and has become throughout the 

 great "corn belt" a serious pest. It is another illustration 

 of man's influence in disturbing the natural balance. Corn 

 fields have replaced the native prairies and woodlands over 

 wide areas, and have offered opportunities for almost un- 

 limited increase in numbers of corn insects that were doubt- 

 less but sparingly distributed before. 



FIG. 41. Small brown ant (Lasius 

 niger alienus) that domesticates 

 the corn root aphis; worker, x 8 

 (from Forbes). 



