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 PERIODICAL CICADA

TI-:E 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 lire 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 bas its definite year of emergence, and in general a pretty well-defined territorv. 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, arAd 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

INSECTS

come