Cicada
In this century of rapid scientific
discovery, there still exist natural
phenomena with the power to inspire
wonder and mystery. The cicada, an insect
known since ancient times, is one
such phenomenon. Because scientific knowledge
of the cicada contains many
gaps, these mysterious insects can still stimulate
our imagination or lead us
into confusion. At the present time, the cicada is
many things to many
people: it is a curiosity that should be approached
scientifically; it is a
source of superstition and dread; it is also little more
than an annoying,
seasonal inconvenience. The cicada is a stout, black insect
about an inch in
length. Various species of this insect can be found all over
North of the
America. When the cicada is at rest, its large, transparent, veined
wings are
folded over the top of its body and extend about a quarter of an inch
beyond
it. Cicada wing veins are and information reddish orange in color, as are
its
eyes and legs. The front legs are sharp and crablike, allowing the animal
to
hold tight to the bark of trees. The species of American cicada most
written
about by scientists and most wondered about by the general public is
known as
the periodical cicada. Its scientific name is Magicicada
septendecim. This
species of cicada appears above ground only once every
seventeen years. What the
cicada does underground for most of its
seventeen-year life span was a mystery
until fairly recently. In the early
part of this century, a man named C.L.
Marlett, who worked for the United
States Department of Agriculture, decided to
find out. He began burying
cicada eggs in his backyard and digging them up
periodically for observation.
He soon found out that the cicada begins life as a
tiny nymph about six
hundredths of an inch in length. A nymph is an immature
insect, before it has
fully developed wings or reproductive organs. During their
sixteen years and
ten and one-half months underground, cicada nymphs are nestled
against tree
roots from which they gently suck the juices. Nourished by this
root sap,
they begin to grow. They shed their skin four times before they reach
adult
size. Once matured, a cicada does not necessarily leave its
underground
nursery. All cicadas of the same generation in a region wait for
a seventeenth
spring before they come creeping forth from the ground as a
group. The eeriness
of this group effort has puzzled humans for centuries.
People have responded to
the mystery with a host of superstitions, educated
guesses, and scientific
theories. One of the earliest explanations for the
mass appearance of cicada
populations after their long absence in an area was
that the insects had come to
foretell war. This idea stems from an
observation of the adult cicada shortly
after it appears above ground. It
immediately sheds its skin for the last time
and begins to darken in color.
Near the outer edge of its front wings, a black
mark appears that looks
distinctly like the letter W. Some thought this W stood
for "war." In the
past, people who saw a group of cicadas emerge from
the ground like an
invading army were filled with panic. The sight was
especially frightening
because literally millions of insects can appear within
an area of a few
square miles. Later explanations for the mass appearance of
cicadas stem from
more scientific observations. Dr. L. L. Pechuman, a professor
at the New York
State College of Agriculture and Life Sciences at Cornell
University, has
suggested that coming above ground only once every seventeen
years is an
excellent way for a species to discourage its natural enemies.
Perhaps
the cicadas have evolved a special kind of biological time clock to
protect
them from predators. James Heath, an insect physiologist at
the
University of Illinois, theorizes that the cicadas all emerge at
around the same
time in a certain year because the soil has reached a
temperature of 64 degrees.
Theories like this have still not been proved
absolutely, but they do a lot to
dispel the fear, awe, or confusion
experienced by many people who witness
millions of cicadas surfacing at once.
Once cicadas surface, they lose no time.
At this point in This their life
cycle, they have only 5 or 6 weeks of life
remaining. They head quickly for
the nearest tree or bush and climb onto it.
Then, holding onto the bark
with their clawlike front legs, they shed their skin
for the last time and
become large-winged adults. These adults will mate, and
the females will then
dig into the tender bark of small twigs to deposit their
eggs. The adult
cicadas die shortly after the mating and egg- laying process has
occurred.
The eggs hatch a few weeks after being laid, thus yielding a new
generation
of nymphs. The nymphs fall to the ground from the trees and then
crawl to the
soil, renewing the 17-year cycle. Opinions remain divided
concerning the
amount of harm done by cicadas to trees and to bushes. The
Pilgrims who
is came to the New World assumed that cicadas were locusts. An army
of
locusts can destroy acres of greenery in record time by biting and
chewing
leaves and stems. To the present day, the Pilgrim misidentification
of cicadas
has stuck, and many people still refer to cicadas as
"seventeen-year
locusts." Millions of plant lovers use the name as an excuse
to fear and
detest cicadas. In reality, cicadas can only suck-not bite-tender
plant tissue;
and adult cicadas eat little if at all during their five to six
weeks above
ground. According to Jane E. Brody, who writes science articles
for The New York
Times, the only harm done to trees by cicadas occurs
during egg-laying. This
egg-laying leads only "to a kind of natural pruning
and an injury that all
but the young trees can easily withstand." However,
Richard Maffei, author
of Insects in Your Garden, strongly disagrees. He
maintains that "leaves on
twigs and branches so punctured usually turn brown,
but hang on as an eyesore
for weeks before the branch breaks and falls to the
ground." Few disagree
with the opinion that the skins shed by cicadas
aboveground are an unsightly
form of natural litter. A book by Peter Farb
called Insects speaks
disapprovingly of the "junk yard of skins" shed by a
swarm of cicadas
in an Indiana orchard in 1953. Jane E. Brody describes a
time in the Northeast
in 1970 when passersby had to "skip like
schoolchildren' to avoid crunching
the piles of cicada bodies beneath their
feet. This litter is added to by birds
who eat the cicadas, spitting out
their wings in the process. For people with
sidewalks to sweep and yards to
clean, such animal remains can be a real
nuisance. This is especially true in
the case of cicadas, as 20,000 to 40,000
can appear beneath a single tree. As
cicada invaders appear, they are also
likely to leave their traces in lawns,
flower beds, and fields. Cicada nymphs
burrowing out of the soil in search of
a tree can leave a hole as large as
one-half inch across. Such honeycombing
of the soil can be very dismaying to
those who take pride in a well-kept
lawn. During a 1987 appearance of cicadas in
the Washington, D.C., area, the
United States Agricultural Research Service was
plagued by telephone calls
from distraught people who wanted to know why their
lawns suddenly had holes.
Of all the phenomena related to cicadas, their song,
or-as some call it-their
racket, has aroused the most comment. Attached to the
underside of a cicada's
abdomen is a pair of large drumheads. These drumheads
are operated by
powerful muscles that set them vibrating. The loud, shrill sound
produced has
been compared to the creaking of an unoiled door hinge, a jet about
to land,
or the sound of a car motor about to break down. Of course, the cicada
sound
with which humans are familiar is actually made by thousands of
cicadas
singing together, and it has a hypnotic, droning effect. Only male
cicadas are
equipped to sing. The noise attracts females, who eventually mate
with their
serenaders. Scientists are beginning to suspect that a very loud
noise, produced
by a giant chorus of male cicadas, is necessary for
successful mating.
Accordingly, small groups of cicadas, which cannot
produce enough noise, tend
not to mate and do not produce a new generation.
The human reactions to cicada
music range from fascinated disbelief to
annoyance to panic. The Guiness Book of
World Records lists male cicadas
as the world's loudest insects maintaining that
their abdominal drums vibrate
at a rate of 7,400 pulses per minute. The noise
produced has been described
by the United States Department of Agriculture as
sounding something like
"Tsh-ee-EEEE-e-ou!" Motorists driving through
a town populated with lovesick
cicadas may stop their cars and open the hood to
find out what is wrong with
the engine. People who sleep during the day-the time
when cicadas sing-often
have to resort to earplugs. Finally, most people realize
that there is no
remedy other than to put up with this sound for five or six
weeks. After all,
it only occurs in a particular area once every seventeen
years. All in all,
the cicada is a creature little understood by most humans.
Throughout the
centuries it has been misnamed or mistakenly feared. Legend has
attributed
terrible powers to it. The cicada has been called everything from a
plague to
an omen of war to a backyard nuisance. Perhaps, in years to come,
as
scientists discover more about this infrequent visitor, it will lose some
of its
mystery. Only then, in the human mind, will it join the familiar ranks
of such
warm-weather insects as the mosquito and the
butterfly.
Bibliography
Brody, Jane E. "After 17 Years, Cicadas
Prepare for Their Roaring
Return." The New York Times, May 12, 1985, pp.
C1, C3. "Cicadas."
The Encyclopaedia Britannica, vol. 3, 1980 ed. Farb,
Peter, and the Editors of
Time-Life Books. The Insects. New York, New
York: Time-Life Books, Inc., 1970.
"The Living World." The Guiness Book of
World Records. New York, New
York: Sterling Publishing Company, Inc.,
1987. Maffei, Richard. Insects in Your
Garden. New York, New York:
Dalton, 1984.