150 



THE STUDY OF INSECTS. 



Dog-day Harvest-fly (Fig. 184) to give an idea of the more 



striking characters of this family. We 

 have several species much smaller than 

 either of these ; but their characteristic 

 form and the presence of three ocelli 

 are sufficient to distinguish them from 

 the members of the other families. 



The Periodical Cicada, Cicada sep- 

 tendecivi (Ci-ca'da sep-ten'de-cim), is 

 very generally known in this country, 

 owing to the great numbers in which 

 it appears, at long intervals of time. 

 This periodical appearance is due to 

 the long time required for the nymphs 

 f.g. 184-cw* tuicen. tQ obtaJn theif growth _either seven- 

 teen or thirteen years — and to the fact that all the members 

 of one generation appear in the adult state at about the same 

 time. The adult female lays her eggs in slits which she 

 makes in the twigs of trees. Small fruit is sometimes in- 

 jured in this way. The eggs hatch in about six weeks. 

 The young nymphs rinding no attraction in a world of sun- 

 shine and of flowers, drop to the ground and bury them- 

 selves in the earth, thus commencing a voluntary seclusion 

 which lasts for years. They live by sucking the juices from 

 the roots of trees. In May of the seventeenth year after 

 their retirement to their earthy cloisters they crawl up to 

 the surface of the ground, like renegade monks ; and, leav 

 ing their nymph-skins clinging to the tree-trunks, like cast- 

 off garments of penance, they come forth, broad-headed, 

 broad-bodied, clear-winged creatures, well fitted to get all 

 the experience possible out of a world whose frivolities they 

 have so long scorned. But, like other creatures, they find a 

 life of dissipation very exhausting, and after a few weeks 

 they sing their last song, lay their eggs, and pass away. 



In the South these insects live only thirteen years under 



