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.

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

17-year Broods		Year				General region
I	Shenandoah Brood	1978	1995	2012	2029	TN, VA, WV
II	East Coast Brood	1979	1996	2013	2030	CT, GA, MD, NC, NJ, NY, OK, PA, SC, VA
III	Iowan Brood	1980	1997	2014	2031	IA, IL, MO
IV	Kansan Brood	1981	1998	2015	2032	IA, KS, MO, NE, OK, TX
V		1982	1999	2016	2033	MD, OH, PA, VA, WV
VI	Brushy Mountains Brood	1983	2000	2017	2034	GA, NC, SC
VII	Onondaga Brood	1984	2001	2018	2035	NY
VIII		1985	2002	2019	2036	OH, PA, WV
IX		1986	2003	2020	2037	NC, VA, WV
X	Great Eastern Brood	1987	2004	2021	2038	DE, GA, IL, IN, KY, MD, MI, NC, NJ, NY, OH, PA, TN, VA, WV
XI		1937	1954	Extinct		CT
XII		Spurious
XIII	Northern Illinois Brood	1973	1990	2007	2024	IA, IL, IN, WI
XIV		1974	1991	2008	2025	KY, GA, IN, MA, MD, NC, NJ, NY, OH, PA, TN, VA, WV
XV		Spurious
XVI		Spurious
XVII		Spurious
13-year Broods
XVIII		Spurious
XIX	Great Southern Brood	1985	1998	2011	2024	AL, AR, GA, IN, IL, KY, LA, MD, MO, MS, NC, OK, SC, TN, VA
XX		Spurious
XXI		1870	Extinct			FL
XXII	Baton Rouge Brood	1988	2001	2014	2027	LA, MS, OH, KY
XXIII	Lower Mississippi Brood	1989	2002	2015	2028	AR, IL, IN, KY, LA, MO, MS, TN
XXIV		Spurious
XXVII		Spurious
XXIX		Spurious
XXX		Spurious