The Strange Cycle of the Cicada
BY HENRY C. McCOOK, D.D., Sc.D., LL.D.
THE true locust of our meadows and fields, which is closely related to the dread destroyer of Holy Scriptures and to the Rocky Mountain locust, is commonly called a "grasshopper," which it is not. The real grasshopper resembles the true locust in many respects, but is a different insect. Then again, the proper name of the so-called "seventeen-year locust" is Cicada (Cicada septendecim), and it belongs to a genus known in Great Britain as "harvest-flies."
There is an annual cicada whose buzzing note is popularly held to predict hot weather, and which in form and habit resembles the seventeen-year species. Since this insect is known to appear from year to year, some persons have doubted the existence of a seventeen-year species on the ground of what they call their own observation. But Septendecim is truly periodical, and takes seventeen years to mature. That time is spent underneath the ground, in an undeveloped condition known as the pupa state. The "shells" are the cast-off pupa-cases, or final "moults," of the insects when they come up after their long sojourn within the earth.
At several points in the United States seventeen-year cicadas appeared in the spring of 1902, while in other parts there were none. This uncovers one of the curious facts in the insect's natural history. Somewhere throughout the continent there appears, almost every year, a brood which is limited to a certain belt of country of greater or less extent. Entomologists, by keeping the track of these broods, have been able to predict their appearance within certain zones. For example, in the western suburbs of Philadelphia immense numbers of cicadas appeared in the summer of 1885. This visit was predicted and announced by the writer several months before it occurred. The only knowledge needed for this was that a brood had appeared in 1868; and the only ability, that of adding seventeen to these figures. In like manner, by adding seventeen again, a 1902 brood was predicted, and it arrived "on time." If readers will make note of the cicadas' coming in their own neighborhood, they may be sure that seventeen years thereafter another brood will appear.
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The Seventeen-year Cicada and
its Pupa-case
We begin our history with the exode of the pupæ from the ground, and will limit it to observations (hitherto unpublished) of the brood of 1885 in Philadelphia. The first pupæ appeared about May 23, but were not out in great numbers until the second week in June. The exode began about six o'clock, evening, and continued during the night, but chiefly the first part thereof. The exit from the burrow was deliberate, as was also the insects' progress over the surfaces
