THE PERIODICAL CICADA

BY
WM. J. GERHARD

Associate Curator of Insects

FIELD MUSEUM OF NATURAL HISTORY

CHICAGO
1923

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PERIODICAL OR
SEVENTEEN-YEAR CICADA

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THE PERIODICAL CICADA.

FROM AN EXHIBIT IN FIELD MUSEUM OF NATURAL HISTORY, SHOWING THE VARIOUS STAGES
OF THE INSECT AND THE INJURIOUS EGG-LAYING HABITS OF THE FEMALES.

FIELD MUSEUM OF NATURAL HISTORY
DEPARTMENT OF ZOOLOGY
CHICAGO, 1923

LEAFLET NUMBER 4

The Periodical Cicada

The Periodical or Seventeen-year Cicada, com-
monly but improperly called the “seventeen-year
locust,” is one of the most noteworthy insects found
in North America. Its sudden appearance at inter-
vals in large numbers in different parts of the eastern
United States, the indescribable din caused by the
multitude of singing males, and the conspicuous evi-
dence of the damage the females do to deciduous trees,
invariably arouse widespread attention and much fear
concerning its destructive habits.

The Periodical Cicada is a true bug and, like the
other members of the order Hemiptera, has a jointed
beak fitted for piercing the tissue of plants. The
name locust, so commonly applied to it, is improper,
because almost since the beginning of history it
has been used to designate wholly different insects,
namely, grasshoppers, which have biting mouth-parts
and which are not closely related to cicadas. The use
of the same name for two dissimilar insects, no doubt,
is the result of confusing the cicadas with the devas-
tating locusts of the old world and the destructive
locusts or grasshoppers of the United States.

Not only is this insect noteworthy on account of
its periodic appearance in immense hordes, but it is
remarkable for the extraordinary duration of its life
in the larval and pupal stages. In the Northern
States its immature stages extend over a period of
seventeen years; in the South, thirteen years are

[41]

2 FIELD MUSEUM OF NATURAL HISTORY

required for its underground existence. It is the
only insect that is known to live for so long a period.
The sound-producing organs of the adult male are
likewise wholly different from those of other insects,
in no way resembling the stridulating apparatus of
grasshoppers, katydids and crickets.

Like most insects, the Periodical Cicada passes
through four stages during its life cycle, namely, the
egg, larval, pupal and adult stages. Although some
of the facts of the life-history were known to the
early colonists, it was only during the latter half of
the last century that much progress was made in
solving many of the problems concerning this inter-
esting cicada. Thus, for a long time it was difficult
to account for the appearance of various broods in
different sections of the country at intervals shorter
than the customary seventeen-year period. The ex-
planation became simple when it was ascertained that
there were two races of this insect, one in the North-
ern States requiring seventeen years for its life cycle,
a southern one developing through all of its stages in
thirteen years.

On account of the difference in the duration of the
life of the northern and southern races, at one time
it was thought that there were two species of the
Periodical Cicada in America. For this reason dif-
ferent specific names were assigned to them. A name
was also proposed for the small, dwarfed individuals
that are found among nearly every brood. But as no
constant, structural characters have been found to
separate the three so-called species, entomologists
now consider them to be one species, which they
designate as Tibicina septendecim, with a southern
race, tredecim, and a small form, cassini.

By means of the many, scattered notes and records,
extending back over two hundred years, and the more

[ 42]

THE PERIODICAL CICADA
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Distribution of the broods of the 17-year race of the
Periodical Cicada (after Marlatt).

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Distribution of the broods of the 13-year race of the
Periodical Cicada (after Marlatt).

[43]

4 FIELD MUSEUM OF NATURAL HISTORY

recent, careful observations, it has become possible
to trace out thirty broods of the Periodical Cicada.
Seventeen broods belong to the northern race; thir-
teen to the southern. These broods vary greatly in
the number of individuals and in the range of their
distribution. For example, Brood XI (1920) is very
small and appears only in a few sections of Massachu-
setts and Connecticut, whereas Brood X (1919) is
recorded from at least fourteen states, in four of
which, namely, Indiana, Ohio, Maryland and _ south-
eastern Pennsylvania, it appears in dense swarms.
Northern Illinois is within the range of only one
large or dense brood, and that is the rather compact
Brood XIII, which was so much in evidence during the
summer of 1922. With the exception of a few records
of individuals in some other states, this brood is
distributed over the northern half of Illinois, eastern
Iowa, southern Wisconsin and Michigan and north-
western Indiana.

The two maps: on the preceding page indicate the
distribution of all the broods of the two races. It will
be noted that the range of the two races overlaps for a
short distance, particularly in southern Missouri, Ken-
tucky, Tennessee, Illinois and Indiana. If the differ-
ence in the duration of the immature stages of the two
races were wholly due to climatic conditions, it would be
natural to expect to find a gradual decrease in the time
of development of the northern race as it approaches
the northern limits of the southern race. This, how-
ever, is not the case. Seemingly the time of develop-
ment, while no doubt originally influenced by climatic
conditions, has become fixed for the species or race as
a whole and is now not permanently modified by
slight differences in temperature. That the duration
of the life of this cicada is sometimes either acceler-
ated or retarded is quite evident, for not infrequently

[44]

THE PERIODICAL CICADA 5

a few adults emerge a year before the main brood is
due, or they may appear a year later.

To account for the existence of the various broods
today, the plausible theory has been advanced that
originally, many centuries ago, there was but one
brood for each of the two races and that they ap-
peared throughout their entire range once every sev-
enteen or thirteen years. But as accelerated or be-
lated individuals increased in number, extended their
range and resumed their normal life cycle, there were
started the various broods that are now recognized.
According to this hypothesis, if the breeding places do
not become too limited and no other detrimental fac-
tors arise, the different broods will increase to such an
extent in the distant future that this insect will appear
every year throughout its entire range.

The newly hatched larve, or young, of the Periodi-
cal Cicada are pale, minute, active creatures with
thick forelegs well-fitted for digging and a jointed
beak well-suited for piercing small roots. On emerg-
ing from the egg, which will be described later, the
young drop lightly to the ground and work their way
into the soil for a short distance. Near some rootlet
each larva encloses itself in a little, isolated, earthen
cell which is enlarged as the young increases in size.
It is not probable that they move about in the ground
for any great distance, but just how they really pass
this long, dark period of their life is not known and
obviously is difficult to ascertain. Since their cells
are nearly always found in close contact to a root or
rootlet, it is believed that the immature cicadas feed
mainly upon the juices of small roots. The depth to
which the larve burrow varies from six to twenty-
four inches. There are, however, records of some that
were found four feet or more beneath the surface of
the soil. During their long, subterranean existence

[45]

6 FIELD MUSEUM OF NATURAL HISTORY

they grow slowly and moult or shed their skin at in-
tervals of several years. Some time after the fourth
moult, when the larve (of the northern race) are
about twelve years old, they change into the first of
their two pupal stages.

The pup of the Periodical Cicada, unlike those of
the majority of insects, rather closely resemble the
larve. They likewise are quite active and continue
to feed upon the juices of roots. Early in the spring,
or during the latter part of April, a few months less
than seventeen years after the young of the northern
race began their subterranean life, the pups, seem-
ingly all of them at the same time, burrow upward
toward the surface of the ground. At first the exit
burrows or cells may end just below the surface,
under logs, stones, chips, or leaves; but under certain
conditions the pupe erect tube-like chimneys or tur-
rets of clay that extend from two to six inches above
the ground.

An astonishingly large number of larve and finally
pupz sometimes inhabit a limited area of the soil. As
many as twenty-five chimneys or turrets have been
found on one square foot of ground, and nine thou-
sand burrow exits have been counted under one tree.

The exodus from their burrows occurs generally
after sundown during the latter part of May and the
fore part of June. During one evening myriads of
pup, as if impelled by an irresistible force, leave
their burrows and turrets and climb up on any nearby
object. Some crawl up on plants less than a foot in
height, while others may ascend trees for a distance
of fifteen or more feet. On reaching a favorable
spot, they rest quietly for a short period, their thick,
front legs clinging tightly to their support. Shortly
after it has become dark, the interesting transforma-
tion begins. A longitudinal slit first appears along

[46]

THE PERIODICAL CICADA 7

the middle of the forepart of the pupa’s back. This
opening gradually widens as the pale adult slowly
emerges and leaves the empty pupal skin attached to a
leaf, twig or branch.

The freshly emerged adults are rather ghostly
creatures, soft, flabby, creamy white in color, with
reddish compound eyes and two, black, rectangular
spots on their back just behind the head. At first
the wings are merely little, wrinkled, whitish pads
with an orange tinge at their base, but they soon ex-
pand to their final size. The entire body then be-
gins to harden and to assume the characteristic color
of the species. A few hours after sunrise on the
morning following their transformation, the adult
cicadas are ready to commence their short but active
career, lasting only from four to six weeks.

Until a comparatively recent date it was believed
that no food was taken by the Periodical Cicada in
the adult stage. It is now known, however, that it
does feed upon the sap of trees,' the branches of which
it pierces by means of its beak. Whether the taking
of food is really essential for mating and egg-laying
is still an open question. For obtaining liquid nour-
ishment its mouth-parts are well fitted. Instead of
having biting jaws, it possesses a jointed, beak-like
lower lip which encloses fine, elongated, stiff, piercing
organs that, with their beak-like sheath, convey the
sap to the mouth cavity. Under favorable conditions,
this insect could readily pierce the human skin by
means of its beak, but apparently it rarely or never
attempts to protect itself in such a manner.

The egg-laying habits of this cicada are of consid-
erable interest, and to them is due most of the dam-
age caused by this insect. The female inserts her
eggs in the twigs and branches of trees by means of
a strong, curved ovipositor which extends from the

[47]

8 FIELD MUSEUM OF NATURAL HISTORY

underside of the abdomen. The main part of the
ovipositor consists of three, horny pieces, two of which
are serrated and spear-shaped at the tip, and by a
backward and forward movement are able to make
a series of punctures in hard wood. Despite a belief
to the contrary, the ovipositor is not a sting, and it is
doubtful whether it is ever used as a means of defense.

The eggs of the Periodical Cicada are whitish,
cylindrical and about one-twelfth of an inch in length.
They are inserted just below the surface and are in-
clined forward at an angle of 45 degrees. With her
ovipositor the female makes a series of punctures,
generally on the under side of the twig, about half an
inch in length, and in them she then lays a longitudinal
row of eggs in pairs. Without changing her position
on the twig, she makes another series of punctures
along side of the first, so that finally each egg nest in
the twig consists of two more or less parallel rows of
eggs, from ten to eighteen in number and separated
by a thin partition. Beginning toward the base of
the twig, which commonly is one of the previous
year’s growth, she works toward the tip, or occasion-
ally toward the base. Sometimes the egg nests are so
close together that they appear to be continuous.
One twig after another is supposed to be pierced in
the manner described until the female has laid her
batch of eggs, which may number from two to six
hundred.

The eggs are laid in a large variety of trees, bushes,
and sometimes in herbaceous plants. Oak trees,
either young or old, seem to be preferred, possibly
because in most woodland tracts they predominate,
and, therefore, are the most accessible. Pine trees
appear to be exempt, the gummy sap exuding from the
punctures, no doubt, being detrimental to the hatch-
ing of the eggs.

[48]

THE PERIODICAL CICADA

1. Egg. 5and 6. Body of males.
2. Newly hatched larva. (Showing sound organs at A)
8. Full grown larva. 7. Body of female.
(Fourth stage) (Showing ovipositor)
4. Pupa (second stage). 8. Adult female.
(Very similar to first stage) 9. Egg nests in twig.

(Figs. 1, 2 and 3 greatly enlarged, after Marlatt; figs. 4-9 slightly reduced.)

[49]

10 FIELD MUSEUM OF NATURAL HISTORY

The results of the cicada’s egg-laying habits vary
with different trees. The oaks show the effects most
conspicuously; the leaves beyond the first punctures
_ turn brown, and many of the twigs become so weak
that they are broken off by the wind. Under the less
hardy oaks the ground is sometimes almost covered
with dead terminal twigs. A few weeks after a
large brood has emerged, tracts of oak woodland ap-
pear as though they had been scorched by a forest
fire. But some trees withstand the effects of the
punctures fairly well, though the egg nests are prone
to leave scars that eventually produce a weak spot
in the growing branch.

The Seventeen-year Cicada fortunately appears
mainly and most abundantly in woodland tracts,
places where its injurious habits do not result in an
appreciable, monetary loss. It likewise does not fly
far from its breeding grounds. Nevertheless, it often
does much harm to fruit trees. This is particularly
the case wherever orchards and nurseries are located
near wooded areas in which the cicadas may be nu-
merous. Not only is nursery stock sometimes badly
injured, but frequently young trees die from the re-
sults of the egg punctures.

A few days after a large brood of cicadas has
emerged from the ground, the air resounds with the
peculiar, whirring noise caused by the countless
males. It is only the male that is capable of making
the characteristic buzzing sound; and no other in-
sects, except those belonging to the cicada family,
have a similar musical apparatus. The sound organs
occupy nearly the entire basal segment of the abdo-
men. The most conspicuous of these organs are two,
covering flaps or opercula, visible only from below,
and two tense, ribbed drum-like membranes which
are vibrated by two powerful muscles. By raising

[50]

THE PERIODICAL CICADA ll

and lowering the abdomen, thereby changing the posi-
tion of the opercula, as well as in other ways, the
nature of the song is changed at will. So distinctive
is the sound produced by the various species of
cicadas, that a student learns to recognize many of
them by their song alone.

The family Cicadidez, of which the Periodical Cicada
is the most noteworthy member, belongs to the order
Hemiptera, which comprises the true bugs or those
insects having a jointed beak fitted for piercing and
sucking. The family is well represented throughout
the tropical and temperate regions: of both hemis-
pheres, over eight hundred species having been
described. Of this number one hundred and thirteen
are listed from America north of Mexico. All of the
females lay their eggs in the tissues of plants or trees;
all of the males have the complex, sound organs, and
are considered to be the noisiest insects in the world;
but, with the exception of the Periodical Cicada, so
far as known, not one of them requires more than two
years for its development from the egg to the adult
stage. The Dog-day Harvest-fly or Lyreman is one of
the common cicadas that is heard every summer. As
it is two-brooded, the adults appear every year.

The cicadas are fairly large, four-winged insects,
with a blunt head, three-jointed beak arising near
the base of the lower surface of the head, prominent
compound eyes, three simple eyes or ocelli, and an ab-
domen consisting of six segments. The front legs
are much thickened and armed with a spine beneath.
The wings are of a similar texture throughout, and
when at rest extend roof-like over the body. In the
tropics many of the species are brightly colored, but
in the United States they are mostly greenish marked
with red and black.

{ 51]

12 FIELD MUSEUM OF NATURAL HISTORY

There is no conclusive evidence apparently that the
immature Periodical Cicada does very much injury to
plants or trees during the long period that it feeds
upon the juices of small roots. It is, therefore, only
in exceptional cases, or in very limited areas, that it
might prove desirable to destroy the young. Accord-
ing to Dr. Marlatt, the most satisfactory method of
killing the larve is the use of bisulphide of carbon in-
jected into the soil where it is known they are quite
numerous.

In the adult stage the females unquestionably are
very harmful to various trees and shrubs, though the
damage they do is probably not nearly so extensive
as is generally supposed. On oak trees, at least, the
results of their egg-laying habits are much in the
nature of a pruning. But in orchards and nurseries
the trees are sometimes injured so severely that some
means of protecting or saving them and destroying
the cicadas must be adopted.

On account of the myriad of individuals over a wide
area and the short life of the adults, the usual methods
of destroying noxious insects are not always practi-
cal. The use of repellents to prevent the females from
ovipositing has likewise not met with much success.
When the adults emerge near orchards or nurseries,
young fruit trees should, if possible, be protected by
netting, and the cicadas resting thereon should be col-
lected and killed every morning and evening, when
they are somewhat sluggish. As the egg nests or scars
often serve as openings for other destructive insects, it
is quite essential to take proper care of young injured
trees. In limited areas, like parks and yards contain-
ing shade trees and shrubbery, the emerging and
adult cicadas can be readily killed by spraying them
with a strong kerosene emulsion. Even the pup are
not immune to an emulsion of kerosene, soap and

[52]

THE PERIODICAL CICADA 13

water. Since the various broods are known to appear
during a definite year in different places, it is obviously
unwise to plant nursery stock or orchards near wood-
land when this insect is soon due.

Although the Periodical Cicada may not appear to
be decreasing in number to the casual observer, there
is sufficient evidence to indicate that it is not nearly
so abundant in many places as it was years ago. Mites
and other insects prey upon it in its various stages,
and very many of the rather helpless adults are de-
voured by birds, especially the English sparrow. But
the most potent factors that are reducing their num-
ber are the diminishing woodland areas and the clear-
ing of land for cultivation. It is, therefore, not im-
probable that in the distant future this long-lived in-
sect may be exterminated by the agricultural devel-
opment of the country.

Wm. J. GERHARD,
Associate Curator of Insects.

[53]

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