THE INSECT WORLD. 



127 



to bees and wasps, who feed greedily upon it, and is yet more 

 tempting to ants, whose relations to plant-lice merit more than a 

 passing notice, since they are of decided economic importance. 



It is a common thing to see ants crawling over leaves infested 

 by plant-lice, and it is often considered well that this should be 

 so, under the erroneous impression that the ants feed upon plant- 

 lice. In some cultivated fields ant-hills abound early in spring, 

 the little mounds scarcely rising above the surface, being seen 

 everywhere. We next find, shortly after, plant-lice infesting the 

 roots or leaves of the growing crop. In truth, ants are protectors 

 of plant-lice ; they are fond of their sweet excretion, and favor 

 their increase and development in every possible way. The 

 plant-lice seem to realize that they have nothing to fear, and 

 readily yield to the ants of their sweets whenever approached for 

 that purpose. Some species of aphids are indeed practically 

 dependent upon ants for their existence. Where some of them 

 lay their eggs we have not yet been able to learn, but perhaps 

 they simply drop them to the ground, where their color and size 

 render them invisible to our eyes. The ants find, gather, 'and 

 carry them into their galleries, where they store them until spring. 

 When vegetation starts and all conditions are favorable, the 

 eggs are taken where they can hatch normally, the young lice 

 being afterward carried to the plants upon which they are to feed. 

 An instance nearly like this, save that the young are carried over 

 winter, we find in the lice infesting corn roots, and undoubtedly 

 there are many others. 



The study of plant-lice is difficult by reason of the matters 

 already set out, and it sometimes requires years to supply a miss- 

 ing hnk in their life history. The differences between them are 

 not always well marked, and the tendency has been to recognize 

 species as distinct when they feed on different food-plants. This 

 basis has proved erroneous, however, and now the wonder is to 

 find how many food-plants a single species may actually have. 



It has been mentioned that a number of plant-lice feed upon 

 roots, and some species pass their entire life underground. Such 

 are the RhizobiincB, which sometimes become distinctly injurious, 

 as, for instance, when they occur on the roots of lettuce, in green- 

 houses and out-doors. Sometimes they are found on the roots 

 of trees or shrubs, quite usually attended by ants, which provide 



