When the proper night comes, in April or May, the nymphs leave the ground in vast numbers and head for upright objects. A tree is the ideal goal if it can be attained. But the transformation from nymph to adult cannot be delayed. If a tree is not within range, a bush or a weed, a blade of grass, or even a post or a telegraph pole, will do. The nymph secures a good hold on the object, splits its nymphal skin along the middle of the back, and laboriously works itself out. The job of shedding the nymphal skin is completed in an hour or less. The cicada is now an adult, but is soft and white. It hardens and becomes darker. In a few hours it is fully mature. The insects mate within a week after becoming adults. A few days after mating, the females lay eggs. The adults live 5 or 6 weeks. Not all cicadas pass through all the stages of development. Many eggs do not hatch. Some nymphs never get established on roots, and some die while trying to shed their nymphal skins. When They Appear Latitude and elevation produce the conditions that determine the date on which cicadas come out of the ground. In some southern areas the period of emergence begins in the last week of April. In some northern areas it begins in the last week of May. Between these early and late extremes, periods of emergence occur elsewhere. The farther north the cicadas are, the later they emerge. The fact that periodical cicadas in the North have a 17-year life cycle, and those in the South a 13-year cycle, should not be interpreted to mean that the insect is seen only at 17-year intervals in the North and only at 13-year intervals in the South. The insects emerge somewhere almost every year. The explanation is that there are different broods, which emerge in different years. [Illustration: Adult several hours after transformation.] Cicadas of the 17-year race that emerge in any given year comprise a brood, those that emerge the next year comprise another brood, and so on. The same is true of the 13-year race. While adults of one brood are singing in the trees, other broods, in different stages of development, are in the soil--perhaps close by, perhaps hundreds of miles away. They will emerge when they have passed their allotted time in the soil. Most of the broods are separated geographically, but some overlap. The number of cicadas emerging in successive years is not maintained at anything like an even level. Four of the 17 "possible" 17-year broods are referred to by such terms as "doubtful," "unimportant," and "almost extinct." We have only scattered records concerning them, and one or more may be extinct. Only two of the 13-year broods are large; a few others exist, but the exact number is not known. In some years two broods emerge--one in the North and one in the South. Where They Appear The range of the periodical cicada covers nearly all the United States east of the Missouri Valley, and includes Arkansas and Louisiana.