THE BUGS: HEMIPTERA 33 



vibration of tightly stretched membranes, somewhat in the 

 way sound may be produced by pushing up and down on 

 the bottom of a tin pan. This note, heard in the middle of 

 hot summer days, has been celebrated as the "song" of the 

 cicada since the time of the Greeks. 



The female lays her eggs in slits, usually in the small 

 terminal twigs of trees, generally causing them to wither 

 and die. In a year in which these insects appear in large 

 numbers the trees look as if a fire had passed over them 

 and scorched the ends of all the twigs. The eggs hatch in 

 about six weeks, and the nymphs drop to the ground, into 

 which they dig, and for a long period of time, thirteen years 

 in the southern states and seventeen years in the North, 

 they lie in a cell feeding on the juices of the roots of trees. 

 Early in the summer of the thirteenth or seventeenth year, 

 they rise to the surface, and, clinging to some convenient 

 support, cast their last nymph skin to come out as winged 

 creatures for their few weeks of adult life. In some cases, 

 when the nymphs reach the surface, they build peculiar 

 cones of clay (Fig. 18) several inches in height, over the 

 mouths of their burrow's, entirely closing the top of the 

 cone. In the upper part of these they wait the period of 

 their final molt. The formation of these structures has been 

 explained by some as due to the prevalence of long-continued 

 wet weather at the time of the emergence ; by others, as 

 occasioned by heating of the ground in certain localities by 

 the sun, thus bringing the nymphs to the surface before their 

 time. 



Aphids. Every one who has tried to keep plants indoors 

 must have noticed the small green, oval insects known as 

 plant-lice, or aphids. There are many species infesting dif- 

 ferent 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 



