The spectacular mass emergences of periodical cicadas (Magicicada spp.) in Eastern North America have long attracted attention. Periodical cicadas are unique in that all (or nearly all) members of the population emerge in one year and then are absent in the intervening years. While any given location sees an emergence just once every 13 or 17 years, different regions emerge on different schedules, so that periodical cicadas are divided into “broods,” or locally synchronized emergences on a common schedule. The broods appear to be mostly parapatric (non-overlapping) and they vary in size from regional to extremely localized.
Periodical cicadas emerge only in the spring, and they are different from the "summer" or "Dog Day" cicadas that are common in many of the same locations in July, August, and September. These cicadas emerge each year, and they are not periodical.
Learn more at The Periodical Cicada Page.