Broods | Periodical Cicada Information Pages (2024)

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 three 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.

About the maps on this site

All of the maps created for this site have similar characteristics and limitations. Unlike many maps of periodical cicadas, we display our data as point data and do not attempt to draw brood boundaries or generalize our data to counties. Brood boundaries are complex on an extremely fine scale and attempts to encircle records with a drawn boundary usually end up overestimating the extent of the periodical cicada emergence. Likewise, maps that generalize to a county level greatly overestimate brood ranges. Such overestimations, in turn, create the false impression of overlaps (sometimes apparently extensive) between broods or life cycles (see Marshall 2001 for a discussion of these points). To reduce any such tendency to overestimate, our maps are intentionally designed to be conservative. Where our maps show the presence of cicadas (“positive” record), then one of the principal members of this project verified that cicadas were present at that place and time. Where our maps show the absence of cicadas (“negative” record), then one of the principal members of this project visited that location and at that time verified that no cicadas were present. Where our maps show no records at all, that is an indication that no member of this project has visited that location.

Note also that the records on our maps include date information. The dates shown do not represent dates of adult appearance; rather, they represent dates on which choruses were active and the area was visited by a principal member of this project. Thus, in any given area, adult emergence may have occurred a week or more earlier than the dates shown on this map.

In the map below, different broods are represented by different colors. Click on any point to see which brood it belongs to. This map may not be reproduced without written permission.

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 only a few cicadas are present are common, but larger unexpected emergences of thousands of individuals have also been reported. Stragglers are almost certainly responsible for reports of “spurious broods” that are not generally recognized. For more information about stragglers, see this page.

Brood Origins

Periodical cicada broods fit together like puzzle pieces, in both time and space. Broods are neither species nor are they populations; they are best described as regional, multispecies groupings of periodical cicadas that emerge on a common schedule. Broods may have complex histories, exemplified by the fact that some broods have geographically separated disjuncts. More subtly, the different species found in any given brood may also have separate evolutionary histories and may have joined the brood at different times or from different sources. The video below describes one simple hypothesis for brood formation drive by climate shocks and temporary life cycle anomalies.

Guide to Periodical Cicada Broods

Click the links to see details of each brood.