THE SEVENTEEN-YEAR LOCUST: ITS LIFE-PERIOD. 1 69 



Stated is really required for the development of the insect from the egg 

 into the perfect winged state. Yet it is a fact well established in 

 science, and must therefore be admitted, although among the three 

 hundred and fifty thousand species of insects known to us, no other has 

 been found to require so long a period for its changes. 



The Insect Seen Almost Annually. 



It is sometimes urged by those who are unable to appreciate the au- 

 thoritativeness of a scientific statement, that we hear of the appearance 

 of these locust visitations at much shorter intervals — in some i)arts of 

 the United States almost every year. 



This is true. I'o go no further back in our records than to the year 

 1850 — from that time to the present the periodial Cicada (it is improp- 

 erly called a locust) has made its appearance in portions of the United 

 States, in each subsequent year to the present included, with the 

 single exception of the year 1873. It will continue to appear during 

 each subsequent year of the century, with three exceptions — 1887, 

 1890 and 1892, which in the chronology of visitations, happen not to 

 be " locust years." 



Why Reported so Frequently. 



The explanation of these almost annual appearances of the species 

 is very simple, and as follows : There are a number of distinct " broods '' 

 within the United States, each embraced within certain geographical 

 localities and limits (although often overlapping one another) in which 

 they appear, and within which they are always true to their appointed 

 time. 



As the limits of these broods do not vary to any considerable extent 

 in their successive returns, it follows that they do not cover the entire 

 country, but that there are portions in which they are never seen. 



A Thirteen-year Brood. 



Not all of these broods, however, are confined to a seventeen-year 

 cycle. The researches of Professor Riley have shown that in the South- 

 ern States, and extending as far northward as southern Illinois, there 

 are also broods that occur regularly at intervals of thirteen years, to 

 which he has given the name of Cicada tredecim. No specific differ- 

 ence, however, can be discovered in the features of the two broods, 

 and he has, therefore, expressed his opinion that the latter is not en- 

 titled to be regarded as a distinct species, but that it should rather be 

 considered as a race, or as an incipient species, to which for con- 

 venience it is desirable to give a distinctive name {Stippleme?^ to the 

 Missouri Reports, 1 881, p. 58). 

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