402 AN INTRODUCTION TO ENTOMOLOGY 



differs also in seldom, if ever, occurring in sufficient numbers to be 

 of economic importance ; but a brood of it appears each year. 



The member of this family that has attracted most attention is 

 the periodical cicada, Tibicina septendecim. This species is commonly 

 known as the seventeen-year locust; but the term locust when applied 

 to this insect is a misnomer, the true locusts beings members of the 

 order Orthoptcra. The improper application of the term locust to 

 this species was doubtless due to the fact that it appears in great 

 swarms, which reminded the early observers in this country of the 

 hordes of migratory locusts or grasshoppers of the Old World. This 

 species is remarkable for the long time required for it to attain its 

 maturity. The eggs are laid in the twigs of various trees; the female 

 makes a series of slits in the twig, into which the eggs are placed. 

 Sometimes this cicada occurs in such great numbers that they seriously 

 injure small fruit trees, by ovipositing in the twigs and smaller 

 branches. The nymphs hatch in about six weeks. They soon volun- 

 tarily drop to the ground, where they bury themselves. Here they 

 obtain nourishment by sucking the juices from the roots of forest and 

 fruit trees. And here they remain till the seventeenth year following. 

 They emerge from the ground during the last half of May, at which 

 time the empty pupa-skins may be found in great numbers, clinging 

 to the bark of trees and other objects. It is at this period that the 

 cicadas attract attention by the shrill cries of the males. The insects 

 soon pair, the females oviposit, and all disappear in a few weeks. 



More than twenty distinct broods of this species have been traced 

 out; so that one or more broods appear somewhere in the United 

 States nearly every year. In many localities, several broods co-exist; 

 in some cases there are as many as seven distinct broods in the same 

 place, each brood appearing in distinct years. There is a variety of 

 the species in which the period of development is only thirteen years. 

 This variety is chiefly a southern form, while the seventeen-year 

 broods occur in the North. 



Family CERCOPID^ 



The Spittle-Insects or Frog-Hoppers 



During the summer months one often finds upon various shrubs, 

 grass, and other herbs, masses of white froth. In the midst of each of 

 these masses there lives a young insect, a member of this family. 

 In some cases as many as four or five insects inhabit the same mass 

 of froth. It is asserted that these insects undergo all their trans- 

 formations within this mass ; that when one is about to molt for the 

 last time, a clear space is formed about its body and the superficial 

 part of the froth dries, so as to form a vaulted roof to a closed chamber 

 within which the last molt is made. 



The adult insects wander about on herbage, shrubs, and trees. 

 They have the power of leaping well. The name frog-hoppers has 



