THE PERIODICAL CICADA 



Tke Broods 



The two races of the periodical cicada, the seventeen- 

 year and the thirteen-year, together occupy most of the 

 eastern part of the United States, except the northern 

 part of New England, the southeastern corner of Georgia, 

 and the peninsula of Florida. The western limits extend 

 into the eastern part of Nebraska, Kansas, Oklahoma, 

 and Texas. In general, the seventeen-year race is north- 

 ern, and the thirteen-year race is southern, but, though 

 the geographic line between the two races is remarkably 

 distinct, there is considerable overlapping. 



While the two cicada races are distinguished from each 

 other by the length of their life cycle, the members of each 

 race do not all appear in the adult stage in any one year. 

 Both the seventeen-year race and the thirteen-year race 

 are broken up into groups of individuals that emerge in 

 different years, and these groups are known as "broods." 

 Each brood has its definite year of emergence, and in 

 general a pretty well-defined territory. The territories of 

 the different broods, however, overlap, or the range of a 

 small brood may be included in that of a larger one. 

 Hence, in any particular locality, there is not always an 

 interval of thirteen or seventeen years between the ap- 

 pearance of the insects; and it may happen that members 

 of a thirteen-year brood and of a seventeen-year brood 

 will emerge in the same year at the same place. 



The emergence years of the principal cicada broods 

 have now been recorded for a long time, and the oldest 

 record of a swarm is that of the appearance of the "locusts" 

 in New England two hundred and ninety-five years ago. 

 A full account of the broods of both races of the periodical 

 cicada, their distribution, and the dates of their emergence, 

 is given in Dr. C. L. Marlatt's Bulletin, already cited, and 

 the following abstract is taken from this source: 



Wherever a well-defined cicada brood appears in a 

 certain year, it is generally observed that a few individuals 



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