THE STUDY OF INSECTS. 
150 
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 - 
tcndccim (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 
Fig. 184.— Cicada tibiccn. Qbtain their 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 finding 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 
