Magicicada broods and distributions
Although nearly all of the periodical cicadas in a given region emerge in the same year, the cicadas in different regions are not synchronized and may emerge in different years. All periodical cicadas of the same life cycle type that emerge in a given year are known collectively as a single "brood" (or "year-class"). The resulting broods are designated by Roman numerals -- there are 12 broods of 17-year cicadas (with the remaining five year-classes apparently containing no cicadas), and 3 broods of 13-year cicadas (with ten empty year-classes). As a result, it is possible to find adult periodical cicadas in almost any year by traveling to the appropriate location. The table below is a guide to the approximate locations of periodical cicada broods. On a local scale, periodical cicadas can be patchily distributed.
Click here for an alternate version of this table organized by brood instead of year.
Click on a brood number in the table below to see a larger-scale map of that brood's range.
Straggling and spurious broods
Sometimes periodical cicadas emerge "off-schedule" by one or more years. This phenomenon is often referred to by the general term "straggling," although straggling cicadas can emerge either later or earlier than expected. Straggling makes it difficult to construct accurate maps of periodical cicada brood distributions, and historical reports of emergences often contain little or no information about how many cicadas were seen. Straggling emergences in which one or two cicadas are present are common; larger unexpected emergences of thousands of individuals have been reported (e.g. Dybas 1969). Stragglers are almost certainly responsible for reports of "spurious broods" that are not generally recognized and that are not listed above.
These maps are intended to portray only approximate, present-day brood distributions. They are based on previously published maps (Marlatt 1923; Simon 1988) and unpublished data. However, they have not been field checked, and they do not portray historical reports of brood emergences. A project is currently underway to make new maps of periodical cicada broods. See the Magicicada mapping project homepage.
Literature:
Marlatt, C. 1923. The Periodical Cicada. United Stated Department of Agriculture, Bureau of Entomology Bulletin 71
Simon, C. 1988. Evolution of 13- and 17-year periodical cicadas. Bulletin of the Entomological Society of America 34:163-176.
Sometimes periodical cicadas emerge "off-schedule" by one or more years. This phenomenon is often referred to by the general term "straggling," although straggling cicadas can emerge either later or earlier than expected. Straggling makes it difficult to construct accurate maps of periodical cicada brood distributions, and historical reports of emergences often contain little or no information about how many cicadas were seen. Straggling emergences in which one or two cicadas are present are common; larger unexpected emergences of thousands of individuals have been reported (e.g. Dybas 1969).
©2011