THE PERIODICAL CICADA
by Dr. J. A. Lintner in his Twelfth Report on the Insects of New York, published in 1897. Dr. Lintner says the turrets are constructed by the nymphs with soft pellets of clay or mud brought up from below and firmly pressed into place, and he records an observation on a nymph caught at work with a pellet of mud in its claws. We may infer, then, that the cicada's style of work as a mason is only a modification of its working methods as a miner, but it appears that no one has yet actually watched the construction of one of the turrets. At emergence time the towers are opened at the top and the insects come forth as they would from an ordinary chamber beneath the level of the ground.
The Transformation
The period of emergence for most of the cicadas of the northern, or seventeen-year, race is the latter part of May. The time of their appearance over large areas is much more nearly uniform than with most other insects, which show a wide variation according to temperature as determined by the season, the elevation, and the latitude. Nevertheless, observations in different localities show that the cicada, too, is influenced by these conditions. In the South, members of the thirteen-year race may emerge even a month earlier, the first individuals of the southernmost broods appearing in the latter part of April.
By some feeling of impending change the mature nymph, waiting in its chamber, knows when the time of transformation is at hand. Somehow nature regulates the event so that it will happen in the evening, but, once the hour has come, no time is to be lost. The nymph must break out of its cell, find a suitable molting site and one in accord with the traditions of its race, and there fix itself by a firm grip of the tarsal claws. At the beginning of the principal emergence period large numbers of the insects come out of their chambers as early as
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