HEMIPTERA 143 



cannot talk back." The sound is made by " stretching and relaxing a pair 

 of corrugated tympana or parchment-like membranes by means of a 

 muscle attached to the center of each." 1 



The strangest freak in all insect life is the periodical cicada or seventeen- 

 year locust (Fig. 113). It is the longest lived of all insects, for while 

 other insects pass from the egg to imago form in a few days or weeks, or, at 

 the most, in one to three years, this insect requires from thirteen to seven- 

 teen years for this development. In the spring the female cuts slits in 

 tender twigs and lays her eggs therein. In about six weeks they hatch 

 and the nymphs spend the required seventeen years, or, in the case of a 

 southern form, thirteen years, in the ground. They feed by sucking the 

 juices of tender roots. In the spring of the seventeenth or the thirteenth 

 year as the case may be they crawl up to the surface of the ground, 



Fig. 113. The seventeen-year Cicada (c) and pupa (a, 6); d, position of 

 eggs (e) ; f, larva. (Riley.) 



undergo their last molting, and emerge as clear-winged cicadas. This 

 insect is a fine example of protective resemblance. One may be within 

 a few inches of a " singing " cicada and not be able to see it, so near the 

 color of the tree trunk or ground is it. The adult life is short. They lay 

 their eggs, sing their songs, and die. 



The plant-lice or aphids (Aphid'idce) are among our most common and 

 destructive pests in the green-house, field, and orchard. There are many 

 species, most of which are small, the largest barely reaching the length of 

 } inch. The small, soft, usually green body is somewhat pear shaped. 

 Wingless forms are most numerous, but there are forms in almost every 

 brood which have two pairs of delicate transparent wings, the anterior 

 pair of which is the larger. " The two wings of each side are usually con- 



1 Kellogg, p. 167. 



