CICADAS, PLANT LICE, AND SCALE INSECTS 33 



plant lice or aphids (Fig. 17). There are many species in- 

 festing different plants, upon the juices of which they feed. 

 Some attack the roots, but the greater number are found 

 upon the foliage. They are 

 generally not more than three 

 millimeters (about an eighth 

 of an inch) in length, with a 

 somewhat pear-shaped body, 

 and with or without wings. 

 In most species there is found 

 projecting from the back a 

 pair of slender tubes, which 

 secrete a sticky, waxen sub- 

 stance. This is probably pro- 

 tective in its nature. 



One of the most interest- 

 ing aphids is the one living 

 on the roots of corn (Figs. 

 18, 19). This aphid {A' phis 

 maidi-rad'icis) has become a 

 domestic animal of one spe- 

 cies of ant. The cornfield 

 ant cares for the eggs of the 

 aphid in its nest through the 

 winter. In the spring when 

 the young aphids are hatched 

 the ants carry them through 



Fig. 17. Aphids on grapevine. 

 (Slightly reduced) 



Underground tunnels and Courtesy of the United States Depart- 

 . . ment of Agriculture 



place them upon the roots 



of weeds. This occurs before the corn is planted. As soon 

 as the corn is sprouted the ants transfer the aphids to the 

 corn roots. There they do much damage sucking the sap. 

 In return for their close attention the ants are paid by 

 securing the honey dew secreted by the aphids. 



