The Harvest Flies or Cicadas 



Life History of the "Seventeen-year Locust" 



(Cicada septendecim, L.J 



This insect, commonly known as the periodical cicada or 

 seventeen-year locust, is taken here because it is the only species 

 of the family whose life history is thoroughly well understood. 

 It is probably not typical in its very extended larval life. In the 

 North this insect remains either as larva or pupa underground for 

 seventeen years. In the South it develops in thirteen years, thus 

 giving rise to two races which are known as the septendecim and 

 tredecim races. The dividing line between the two races corre- 

 sponds fairly well with the northern margin of the so-called lower 

 austral life zone. In some localities confusion arises from the 

 fact that the insect makes its appearance at shorter intervals than 

 seventeen years. This is accounted for by the fact 

 that the insect appears in distinct broods some of 

 which overlap the territory also inhabited by other 

 broods. There is no reason, however, to suppose 

 that the length of life of any larva is of shorter dura- 

 tion than seventeen years in the North and thirteen 

 in the South. The largest of the Northeastern broods 

 made its last appearance in 1902, and is due again 

 in 1919. It will then be found in great numbers 

 throughout New Jersey, Delaware, part of Pennsyl- 

 vania, Maryland, northern Virginia, Ohio, southern 

 Michigan, Indiana, eastern Illinois, Kentucky and 

 down the Appalachian chain of mountains through 

 North Carolina into northern Georgia. It will also 

 appear in a few localities in Vermont, New York, Wis- 

 consin, West Virginia and Tennessee. 



The eggs are laid in small twigs and branches 

 which are pierced by the ovipositor and in this way 

 the insect does practically the only damage which it accom- 

 plishes. They occur in enormous swarms and the weakening of 

 the twigs, caused by the punctures, causes many of them to be 

 broken off by the wind. The young ant-like larva hatches from 

 the eggs a few weeks after oviposition, escapes from the wounded 

 limb, falls to the ground and burrows quickly out of sight, where 

 it forms for itself a little underground chamber near some rootlet, 



233 



