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American Entomologist • Volume 61, Number 4 245
The periodical cicadas (Magicicada spp.) of east-
ern North America are subdivided into “broods”
or locally synchronized populations that share a
common emergence schedule. Twelve extant broods have
17-year life cycles and three have 13-year cycles. Most
broods contain three morphologically distinct species. In
the late 19th century, Charles Marlatt (1898) published a
groundbreaking series of maps and emergence schedules
accompanied by a sequential numbering scheme des-
ignating the 17-year brood that emerged in 1893 “Brood
I” (with other potential 17-year broods numbered up to
XVII), and the 13-year brood that emerged in 1894 as
“Brood XIX” (with potential broods up to XXX). Later
editions of Marlatt’s work (1907, 1923) added more dis-
tributional records. Marlatt’s maps have long been the
basis for hypotheses concerning brood and species for-
mation (Lloyd and Dybas 1966; Lloyd and White 1976;
Simon and Lloyd 1982). Recent research has focused
on improving the resolution of brood maps beyond the
county-level scale of earlier work (Simon 1988; Cooley
et al. 2004; Cooley et al. 2009; Cooley et al. 2011; Cooley
et al. 2013a; Cooley 2015).
Broods form when periodical cicadas emerge o-sched-
ule in numbers sucient to survive predators and estab-
lish new, self-sustaining populations. Broods are dynamic;
the cluster of Long Island broods was rst documented
by museum specimens in the early 1900s, but in recent
years, emergences of all but Brood XIV appear to be
extinct or decreasing each generation to levels that can-
not support ongoing periodical cicada populations (C.
Simon, unpublished observations; Simon and Lloyd 1982;
Cooley et al. 2011). Likewise, Brood VII has undergone
a rapid range contraction (Cooley et al. 2004). e evo-
lutionary origins of individual broods can be complex;
while some broods appear to have formed in a single
event (a monophyletic origin; Simon 1983), other broods
appear to contain independently derived sub-populations
(Simon and Lloyd 1982; Sota et al. 2013; Cooley 2015).
Furthermore, in most cases, the morphologically distinct
periodical cicada species (up to four) within each brood
have independent evolutionary histories (Sota et al. 2013).
Clues about the processes underlying brood and species
formation and their relation to climate may be encoded in
brood distributions and boundaries (Cooley et al. 2013a).
A new generation of Magicicada brood maps has been
constructed using GIS technology, automated data col-
lections by experts, and Internet-based crowdsourcing
(Cooley et al. 2004; Cooley et al. 2009; Cooley et al. 2011;
Cooley et al. 2013a; Cooley et al. 2013b; Cooley 2015).
Although these maps support the general brood distri-
butions proposed by Marlatt (1923) and Simon’s (1988)
revisions, they include some surprises. For example,
Brood I contains a large, previously unreported disjunct
population in southwestern Virginia and northeastern
Tennessee, separated by a gap of over 200 km from the
main body of the brood in the Shenandoah Valley (Cooley
2015). is disjunct was rst revealed by reports submit-
ted by the general public.
Brood II is one of the geographically larger broods
of periodical cicadas. It adjoins or is thought to be in
e Distribution of Periodical Cicada
(Hemiptera: Cicadidae: Magicicada)
Brood II in 2013:
Disjunct Emergences
Suggest Complex
Brood Origins
JOHN R. COOLEY, CHRIS SIMON, CHRIS T. MAIER, DAVID MARSHALL,
JIN YOSHIMURA, STEPHEN M. CHISWELL, MARTEN EDWARDS,
CHUCK HOLLIDAY, RICHARD GRANTHAM, JOHN ZYLA,
ROBERT L. SANDERS, MICHAEL NECKERMANN, AND GERRY BUNKER
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246 American Entomologist • Winter 2015
proximity to a large number of other
broods (17-year I, IV, VI, IX, X, XIV, the
13-year XIX, and the extinct 17-year XI).
Therefore, a detailed map could pro-
vide additional insights into the nature
of brood origins and boundaries. In all
earlier maps, Brood II is depicted as east
of the Appalachian Mountains from north-
eastern Georgia to the Hudson Valley
and the Connecticut River Basin (Simon
1988). Our map, based on both directly
obtained and crowdsourced records, is
the most detailed to date, and it reveals
a second case of unexpected, previously
unmapped brood disjunction.
Methods
In 2013, we mapped emergences of Brood
II using methods similar to those used for
mapping other Magicicada broods (Cool-
ey et al. 2004; Cooley et al. 2009; Cooley
et al. 2011; Cooley et al. 2013a; Cooley et
al. 2013b; Cooley 2015). We collected 8,644
datapoints with handheld GPS units or
automobiles with GPS dataloggers between
21 May and 1 July 2013. In order to maxi-
mize coverage in the most e cient manner,
each member of our team concentrated
on speci c geographic regions of Brood
II. When possible, information about the
density of periodical cicadas was recorded
using four categories: (0) no cicadas pres-
ent; 1) scattered or single individuals pres-
ent; 2) light choruses (no gaps in the cho-
rus sound); and 3) dense choruses (Cooley
et al. 2013a). All data were processed using
ArcGIS 9.3 software (ESRI 2009).
As before, the website www.magici-
cada.org collected unveri ed (“crowd-
sourced”) periodical cicada sightings
submitted by the general public from
April-June 2013. e distribution of Brood
II contains several major metropolitan
areas along the eastern seaboard. Crowd-
sourcing was especially useful for map-
ping these areas, which include Staten
Island, northern and central regions of
New Jersey, and the outskirts of both
Washington, DC, and Richmond, VA.
Before, during, and after the emergence,
periodical cicadas were publicized in
print media (e.g., e New York Times,
e Wall Street Journal, Washington Post,
National Geographic, e Atlantic, Sci-
ence News), by radio and television (e.g.,
WNPR, WNYC, CBC, PBS, NBC, FOX),
and on the Internet (e.g., Cicadamania,
Wikinews). In addition, several local and
regional “citizen science” initiatives were
launched, including a project organized
by WNYC’s Radiolab that mapped soil
temperatures to predict emergence times.
e extensive media exposure of the 2013
emergence made it an ideal year to col-
lect crowdsourced records.
Each datapoint collected in 2013 was
assigned a “con dence” score (Cooley
2015). We rst discarded all crowdsourced
records that fell outside the United States,
all records taken after 1 July 2013 (when
the last verified record was taken by
one of the authors), and all records in
which the additional comments included
descriptions of cicadas that were clearly
Fig. 1. 2013 records of Brood II (green circles) and veri ed absences of Brood II (small gray cir-
cles) superimposed on Simon’s (Simon 1988) map of the same brood (black circles).`
Fig. 2. 2013 records of Brood II (green circles)
and veri ed absences of Brood II (small gray
circles) superimposed on 2013 crowdsourced
records (green diamonds). Hue and size of green
diamonds re ects con dence, calculated as
described in text. Small, light green diamonds
fall into bottom quartile of con dence values;
large, dark green diamonds fall into the upper
three quartiles.
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American Entomologist • Volume 61, Number 4 247
non-periodical or noted that no cicadas
were present. After editing, the dataset
contained 3,308 crowdsourced records.
We then produced a map that contained
all veri ed positive and negative records
of Brood II from all years in the periodi-
cal cicada database (http://hydrodictyon.
eeb.uconn.edu/projects/cicada/). All ver-
ified negative records were assigned a
“con dence” of 0, and all veri ed posi-
tive records a “con dence” of 1. For each
crowdsourced datapoint, a “standard-
ized proximity score” and a “standard-
ized neighborhood point density” were
used to calculate a “weight” or con dence
score (Cooley 2015). e weighting of each
crowdsourced record fell between 0 and
1 and re ected its proximity to veri ed
positive records and its degree of clus-
tering with other crowdsourced records.
Crowdsourced records that were clustered
or near veri ed records received higher
scores, while isolated records far from
veri ed records received lower scores.
Results
e emergence of Brood II in 2013 large-
ly conformed to the region presented
by Simon (1988), although the brood
appears best represented as a series of
disjunct clusters of populations (Fig. 1).
Our map reveals a patchy distribution
of populations stretching from Geor-
gia to New York and Connecticut and
expands the known distribution of Brood
II to include a large, disjunct region on
the eastern edge of the Great Plains in
central Oklahoma. Because data were
collected primarily from vehicles, our ver-
i ed records tend to appear as strings of
records that follow established roads, even
though the actual distribution includes
areas away from roads. Crowdsourced
records for Brood II were found through-
out the eastern U.S. (Fig. 2), although
they were most concentrated in areas in
which we collected verified records of
periodical cicadas.
e southernmost disjunct emergence
of Brood II was in White County, GA, in
a region where isolated populations of
Broods VI (2000), X (2004), and XIV (2008)
have been recorded, as well as the main
body of Brood XIX (Fig. 3). Brood II was
widely present in the Piedmont regions of
the central seaboard states, with popula-
tions that were sometimes sparse, wide-
ly scattered, or separated by large gaps;
exceptions included dense populations of
M. cassini more or less continuously found
between Charlottesville and Fredericks-
burg, VA, where there were also dense pop-
ulations of M. septendecim (Fig. 4). Near
Lynchburg VA, the edge of Brood II may
overlap the edge of Brood I by up to 5 km;
there was a similar overlap near Moneta,
VA. Brood II overlapped earlier records of
Fig. 3. 2013 records of Brood II (green circles) and veri ed absences of Brood II (small gray
circles), with crowdsourced records (green diamonds, as in Fig. 2) in northeastern Georgia rela-
tive to veri ed records of Broods X (orange triangles) and XIV (red triangles) and crowdsourced
records (green diamonds; hue re ects con dence as above). County names (large text) and place
names (small italic text) are included.
Fig. 4. 2013 records of Brood II (green circles)
and veri ed absences of Brood II (small gray
circles), with crowdsourced records (green dia-
monds, as in Fig. 2) in seaboard states relative
to veri ed records of 17-year Broods I (blue
triangles), IX (brown triangles), X (orange trian-
gles) and XIV (red triangles), and 13-year Brood
XIX (inverted gray triangles). Other broods have
been omitted for clarity.
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248 American Entomologist • Winter 2015
Brood X by up to 15 km near Manassas,
VA (Fig. 4); in each of these cases, the two
broods involved occupied the same trees
(Cooley et al. 2009; Cooley 2015).
In central New Jersey and to the north
of Pennsylvania’s Lehigh Valley, Brood II
was in contact with mapped locations of
Broods X and XIV, although we did not
document any overlaps (Fig. 5). In PA, the
southern border of Brood II roughly fol-
lowed the Kittatinny Ridge (known locally
as Blue Mountain) and extended from
the Delaware Water Gap to a few miles
short of the Susquehanna River. Extremely
dense populations were observed along
the length of the Kittatinny Ridge and in
regions immediately to the north. Popu-
lations in the Pocono Mountain region of
northeastern Pennsylvania were sparse.
All of the observed Pennsylvania popu-
lations were M. septendecim.
North of New York City, Brood II fol-
lowed the Hudson River to just south of
Albany, NY (Fig. 6). Emergences in this
portion of the brood were often sparse
or separated by large gaps, although we
found that some locations in the Hud-
son Valley (such as Bard College) had
remarkably high emergence densities, an
observation backed up by the results of
Karban’s (2014) multigenerational survey.
Notably, all three 17-year species were
found in the Hudson Valley; M. septen-
decula has been absent from the north-
ern portions of other broods we have
surveyed [e.g., III (Cooley et al. 2013a);
VII (Cooley et al. 2004); X (Cooley et
al. 2009); and XIV (Cooley et al. 2011)].
Brood II followed the Connecticut River
Basin from East Haven to Farmington, CT
(Fig. 7); some emergences in Connecti-
cut were extremely sparse or scattered,
though isolated high-density pockets also
occurred in Southington, Meriden, Berlin,
and North Branford, CT. No populations
were found that connected this Connecti-
cut portion of Brood II to any other. All
but one population found in Connecticut
consisted exclusively of M. septendecim;
one isolated pocket of M. septendecula
was found in North Branford, CT (Maier
2015). No populations of M. cassini were
found in the state (see also Maier 1982).
The most surprising finding was an
additional disjunct emergence of Brood
II in Oklahoma (Fig. 8). While Brood II
was emerging in the East, an unusually
large number of crowdsourced records
were submitted to the website from areas
in the vicinity of Moore and Oklahoma
City, OK. We confirmed these reports
and mapped the emergence to the extent
possible. Only M. cassini was found in the
2013 Oklahoma emergence.
Discussion
Although the majority of the crowd-
sourced records fall in or close to areas
where we collected verified records of
Brood II emergences, a signi cant num-
ber of crowdsourced records fall outside
the known distribution of Brood II, espe-
cially in urban areas. is general pattern
Fig. 5. 2013 records of Brood II (green circles) and veri ed absences of Brood II (small gray
circles), with crowdsourced records (green diamonds, as in Fig. 2) in the Susquehanna Valley
relative to veri ed records of 17-year Broods X (orange triangles) and XIV (red triangles). Coun-
ties are denoted in small text. Other broods have been omitted for clarity.
Fig. 6. 2013 records of Brood II (green circles)
and veri ed absences of Brood II (small gray
circles), with crowdsourced records (green dia-
monds, as in Fig. 2) in the Hudson Valley relative
to veri ed records of 17-year Broods X (orange
triangles) and XIV (red triangles). Counties are
denoted in small text. Other broods have been
omitted for clarity.
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American Entomologist • Volume 61, Number 4 249
has emerged in previous brood mapping
e orts (Cooley et al. 2009; Cooley et al.
2011; Cooley 2015). In aggregate, crowd-
sourced records capture the general out-
lines of broods, but individual records are
unreliable, especially if they are isolated
outliers. us, crowdsourced records, at
least in the way that we have collected
them, must be interpreted with extreme
caution and should not be used as the sole
basis for claims about brood distributions.
One unanticipated nding of this study
was that Brood II slightly overlaps Broods
I and X. Although same-cycle brood over-
lap has not been well documented, some
examples are known [e.g., Broods X/XIV
Fig. 8. 2013 records of Brood II (green circles) and veri ed absences of Brood II (small gray circles), with crowdsourced records (green diamonds, as in
Fig. 2) in Oklahoma. Counties are denoted in large text; cities in small text.
Fig. 7. 2013 records of Brood II (green circles)
and veri ed absences of Brood II (small gray
circles), with crowdsourced records (green dia-
monds, as in Fig. 2) in the Connecticut River
Basin. Counties are denoted in large text; cit-
ies in small text.
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250 American Entomologist • Winter 2015
(Lloyd and White 1976, Kritsky et al. 2005,
Cooley et al. 2009, Cooley et al. 2011);
Broods I/XIV on Long Island (Simon et
al. 1981; Simon and Lloyd 1982)], and still
other areas of overlap are suspected [e.g.,
records of Brood I are found in Douthat
State Park, VA, a known collecting local-
ity for Brood V (Cooley 2015)]. Patterns
in the temporal and spatial overlaps of
same-cycle broods, in which apparent-
ly broad overlaps exist between broods
separated by four years, have led to the
“four-year coexistence hypothesis,” in
which competitive interference prevents
broods with less than four years’ tempo-
ral separation from overlapping spatially
(Alexander and Moore 1962; Lloyd and
Dybas 1966; Simon 1979; Simon and Lloyd
1982; Simon 1988). However, the over-
lap between Broods I and II in central
Virginia runs counter to this hypothesis.
is anomaly could be an example of a
“straggling” or o-cycle emergence, in
which cicadas that emerged in 2012 and
2013 both belonged to a single brood,
either Brood I or Brood II. Attribution of
these records to straggling would be most
plausible if, in cases where overlapping
broods are separated by one year, the
small overlapping edges were found to
contain sparse populations of the later-
(or earlier-) emerging brood, and sur-
vivorship of sparse populations is low.
Unfortunately, we do not have quantita-
tive measurements of population densities
in the overlaps between Broods I and II.
Older maps of Brood II (Marlatt 1923;
Simon 1988) do not convey the degree
to which the brood consists of several
well-separated fragments, nor do older
maps indicate that some areas that appear
to contain Brood II include only sparse,
low-density populations. Broods with dis-
junctions are either fragmented relicts of
previously more widespread distributions,
or they are the products of independent
origins and incidental synchronization
(Simon and Lloyd 1982). Local extinc-
tions could explain the separation between
Connecticut River Basin populations and
Hudson River Valley populations or the
patchy nature of Brood II populations in
Virginia. However, other discontinuities in
Brood II are not explainable as products of
local Magicicada extinctions. For instance,
between New York City and Washington,
DC, Broods II and X interdigitate, leaving
both of their distributions discontinuous.
Extinction seems unlikely because the area
appears to be more or less continuously
inhabited by periodical cicadas belonging
to several different broods. As another
example, in northeastern Georgia, Brood
II populations are associated with a cluster
of 17-year brood fragments (II, VI, X, XIV)
all disjunct from the main bodies of their
respective broods and separated from each
other by gaps of four years. Like the brood
cluster on Long Island (Simon and Lloyd
1982), these broods could have been inde-
pendently derived from each other by a
series of four-year accelerations (Lloyd and
Dybas 1966) that occurred independently
of the events leading to the formation of
the main bodies of each of the broods.
e Oklahoma segment of Brood II is
surprising because its location, on the far
western edge of the Magicicada distribu-
tion, is so distant from the main body of
the brood, strongly suggesting an inde-
pendent origin. Marlatt’s maps (1923)
show only isolated county records for
Brood II west of the Appalachians and
no records west of the Mississippi River.
Furthermore, Marlatt gives no indica-
tion that any periodical cicada brood
of either life cycle is present in central
Oklahoma. Much of Marlatt’s original
data came from eld agents of the U.S.
Department of Agriculture (USDA) and
employees of the U.S. Postal Service (Riley
1885; Marlatt 1898, 1907, 1923). In addi-
tion, before its 1907 statehood and during
the main period of USDA record-gather-
ing on periodical cicadas, central eastern
Oklahoma consisted of Native American
lands not under direct control of the fed-
eral government and with little, if any,
USDA infrastructure. Presumably few,
if any, pre-statehood reports of period-
ical cicada emergences were submitted
to the USDA, which could explain the
absence of Oklahoma Brood II records
from Marlatt’s maps. Records of Brood
II were collected shortly after statehood;
the Oklahoma State University collection
contains Magicicada specimens collected
in 1928 and 1979 from Paine and Lincoln
Counties, OK, and the existence of Brood
II in Oklahoma was mentioned in a bro-
chure published by the Oklahoma Coop-
erative Extension Service (Arnold et al.
2008). Due to accidents of timing, these
records were never included in published
maps of periodical cicada broods, and
these records were not noticed by later
studies updating or improving Marlatt’s
maps, including those of Alexander and
Moore (1962), Dybas and Lloyd (1974)
and Simon (1988).
It is possible that additional disjunct
populations remain to be discovered in
Oklahoma, because there is still a large
region where no Magicicada records have
been mapped extending east from the
2013 Brood II segment in central Okla-
homa to the nearest 13-year populations
of Brood XIX near the Arkansas border
(Simon 1988). North and south of this
region, the 13- and 17-year broods (XIX
and IV) make nearly continuous geograph-
ic contact, with no known gaps, and there
is no obvious habitat dierence in the gap
region to suggest absence of Magicicada.
In 2012, a similar region “empty” of period-
ical cicadas in the historical maps turned
out to contain undocumented Brood I
populations in central Appalachia, as
revealed by crowdsourcing (Cooley 2015).
An increasing body of genetic evidence
suggests complex origins for many period-
ical cicada broods (Simon and Lloyd 1982;
Martin and Simon 1988; Martin and Simon
1990; Simon et al. 2000; Cooley et al. 2001;
Sota et al. 2013), a nding corroborated by
the discovery of independently derived
brood clusters on Long Island (Simon and
Lloyd 1982), widely separated disjuncts in
Brood I (Cooley 2015) and Brood II (this
study), and the existence of disjunct brood
clusters in northeastern Georgia (Cooley,
Marshall, and Simon, unpublished data).
Taken together, these ndings demonstrate
that brood formation in periodical cicadas
could be more common than previously
thought, and that many patterns of biodi-
versity within Magicicada remain cryptic.
Uncovering more cryptic diversity is the
key to understanding the historical pro-
cesses that have created both the broods
and the Magicicada species.
Acknowledgments
e National Geographic Society’s Com-
mittee of Research and Exploration
Older maps of Brood II
(Marlatt 1923; Simon 1988)
do not convey the degree
to which the brood consists
of several well-separated
fragments, nor do older
maps indicate that some
areas that appear to contain
Brood II include only sparse,
low-density populations.
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American Entomologist • Volume 61, Number 4 251
provided funding that supported the proj-
ect “Making Modern Maps of Magicica-
da Emergences.” James E. Cooley assist-
ed with the design and construction of
the second-generation GPS dataloggers
used in this study. Invaluable assistance
was provided by John Knox, Don Simon,
Laura Simon, and trained volunteer sur-
veyors assembled by the Connecticut
Department of Energy and Environmental
Protection (DEEP). is work was par-
tially supported by the National Science
Foundation under Grant Nos. NSF DEB
0720664 and DEB 0955849 to Chris Simon.
Any opinions, ndings, and conclusions
or recommendations expressed in this
material are those of the authors and do
not necessarily reect the views of the
NSF. Chris Maier was supported in part by
the Connecticut DEEP. Full records, many
with species information, are available
on the Cicada Central database (http://
hydrodictyon.eeb.uconn.edu/projects/
cicada/databases/databases.php).
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John R. Cooley, Chris Simon, and David Mar-
shall are members of the Department of Ecol-
ogy and Evolutionary Biology, e University
of Connecticut, Storrs CT USA -.
Chris T. Maier is a research scientist in the
Department of Entomology, e Connecti-
cut Agricultural Experiment Station, New
Haven CT USA -. Jin Yoshimura
is a faculty member in the Department of
Systems Engineering, Shizuoka University,
Hamamatsu, Japan. Stephen M. Chiswell is
a research scientist at the National Institute
of Water and Atmospheric Research Limited,
PO Box , Wellington, New Zealand.
Marten Edwards is a faculty member in the
Department of Biology, Muhlenberg College,
Allentown PA USA . Chuck Holliday is
Professor Emeritus in the Department of
Biology, Lafayette College, Easton PA USA
. Richard Grantham is the Director of
the Plant Disease and Insect Diagnostic Lab,
Entomology and Plant Pathology, Oklahoma
State University Stillwater, OK USA .
John Zyla runs the mid-Atlantic cicadas
webpage (cicadas.info). Gerry Bunker runs
the Massachusetts Cicadas website (http://
www.masscic.org). Rober t L. Sanders and
Michael Neckermann are cicada enthusiasts
who have tracked down many cicadas over
the years. e Mapping Project webpage is
www.magicicada.org.
DOI: 10.1093/ae/tmv070
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