American Museum of Natural History.
It is not so easy for us to exhibit the
habits of these interesting creatures,
but I wiU try to suggest some of them

206



tonight and I invite j'ou to become even
better acquainted than you are mth
God's out-of-doors, where these habits
are on exhibition day and night, winter
and summer.

Recently the Westinghouse Com-
pany announced the invention of a
new type of microphone intended pri-
marily for use in broadcasting programs
by radio, but the men in the Research
Department of that progressive com-
pany saw the possibHty of using it to
stud3' the sometimes faint sounds made
by insects. Furthermore, insects have
antennse, and some students, probably
influenced by the fact that your aerial
and mine are caUed antennge, have
suggested that insects send and re-
ceive messages by a method some-
what similar to radio. PersonaUy, I
doubt this, but I have lived so long in
an open-minded, scientific atmosphere,
that I am wilHng to admit the possi-
bility of any idea that has not been
disproved. At any rate, I think that a
radio audience will be interested in the
sound-making habits of insects, and so
I have selected that as my special
topic for this evening.

There is scarcely a grass-plot in the
United States that does not contain
crickets. At certain seasons of the year
some of these crickets become musical
and the air is filled with chirps, usualh'
cheerful but occasionally sounding sad
and lonesome. How do the crickets
chirp and why do some of them chirp,
while others are silent?

I must teU you first that the female
cricket has a long, shm, needle-like
affair at the end of her body and that
with this she places her eggs under the



INSECT SOUNDS



207



surface of the uiiouiul. Tlic yoimii;
cricket as it leaves its uiuler^roiind nest
looks much like an adult cricket except
that it is very small and has no wings.
Like Mr. Finney's turnip this cricket
''grows and it grows." From time to
time as it grows it sheds its skin but it
does not get wings imtil the last molt,
when it is fully grown.

The reason for explaining all of this
is that crickets chirp b}^ rubbing their
front wings together. Near the front
of each front wing of a male cricket
(but not of a female) is an enlarged rib
or brace. On the under side of this rib
is a series of small teeth. Then, on the
upper side of each front wing is a small
rough spot so placed that when the
wings are rubbed together the teeth on
the under side of one wing scrape on
the rough spot that is on the upper side
of the other. If your rheostats and
dials can spare you for a moment,
stretch your hands out in front of you
with the palms up. Now, let the
knuckles of your right hand represent
the file on the underside of a cricket's
front wing and rub these knuckles on
the callouses at the bases of the fingers
of your left hand. That is the idea but,
of course, there is no sound produced
because your hands are not thin mem-
branes like the cricket's wings. In the
case of the cricket this rubbing of a
filelike structure on a rough spot
sets both wings to vibrating very
rapidly, probably at a rate of not fai-
from 15,000 shakes per second. This
rapid vibration of the wings up and
down as the male cricket rubs them
against each other from side to side sets
the air to vibrating in waves of such a
character and frequency that our ears
recognize a shrill sound or chirp. I
have here a file and a thin piece of tin
and I am going to rub one against the
other ( — ) . The tone is not the tone of



a ci'ickct 's chiip hi'caiisc t he t in has not
the same (lualitios as a cricket's wing,
but the sound is produced in exactly the
same way. Katydids are near relatives
of crickets and play the same sort of
instrument. Their favorite selection is
something like this ( — ). The effect
of this rapid vibration of the cricket's
or of the katydid's wings seems to be
exactly the same as that caused when
electrical impulses rapidly vibrate the
diaphragm of oui- telephone receivers.
A difference is that, so far as we know,
there is nothing electrical about either
the cricket's chirp or the katydid's
song. They are purely mechanical.

Now, an interesting point is that only
the male cricket has this apparatus and,
of course, not even the male has it
until it is adult and has fully developed
wings. Young crickets are "seen but
not heard" because they have no wings
and female crickets keep quiet, even
when they are adult, because they can-
not do otherwise, for their wings have
no sound-producing attachments. An
old Greek poet whose wife was prob-
ably different from mine knew about
the prevailing silence of female insects
and wrote concerning one kind :
Happy are cicadas' lives
For they all have voiceless wives.

So much for the sound-production
by crickets, their transmitters. What
are their receivers hke? You receive
sounds by feeling the vibrations of ver\^
small diaphragms, one located on each
side of your head. I do not mean the
diaphragms of your telephone head-set,
if you are using one, for, as far as j'ou
personally are concerned, the phones
are still a part of the transmitting
system. I mean j^our ears and more
particularly your ear-drums. Appar-
ently crickets also have sound-receiving
diaphragms or ear-drums but they are
on the front legs and not on the head.



208



NATURAL HISTORY



The next time you see a cricket, catch
it. Look on the second main joint of
either of the front legs and you ought
to be able to detect a small white spot.
If you examine this spot with a micro-
scope, you will see that it is really a
small diaphragm set into the leg. It is
supposed to be an ear and, if it really
is an ear, both males and females can
hear. We do not know how much they
can hear but presumably they can at
least hear other crickets chirping.

Tree-crickets, katydids, and all of
the grasshopper tribe that, like katy-
dids, have very long antennae, make
sounds in the same way that ordinary
crickets do, and they all have much the
same sort of receiving apparatus. On
the other hand, the grasshoppers that
we commonly see, those having short
antennse, are different. Some of them
make no sounds that we can hear and
apparently have no sound-producing
apparatus. Possibly the new micro-
phone will reveal sounds made by them
and then we will try to discover how
these to us inaudible sounds are made.
Others of these short-horned grass-
hoppers make rasping sounds by
rubbing their hind legs against their
front wings. Still others make loud
sounds by rattling their wings together
as they fly. I have here a wooden
contraption that we used to call a
''razzle-dazzle" or ''policeman's rat-
tle." As you twirl it, two thin pieces
slap against large cogs and make the
noise you will hear shortly; but,
first, hft off your ear-phones if you
are using much amplification. ( — )
That noise was made by use of
exactly the same mechanical prin-
ciple that certain grasshoppers em-
ploy. When I bought this "razzle-
dazzle" last week, a man in the shop
remarked that I must be going to a
wedding. I was not, but the man's



remark was curiously close to a scien-
tific teaching. The grasshoppers that
make sounds in this way are, we think,
hoping to go to weddings and they
plan to be the bridegrooms. The
prospective bride is sitting quietly in
the grass as her lover flutters in the air
above her and rattles his castanets.

A peculiar thing about the receiving
apparatus of these short-horned grass-
hoppers is that the receiving dia-
phragms or ear-drums are not on the
legs as they are in their close relatives,
the crickets and long-horned grass-
hoppers, but on the abdomen, one on
each side near the base.

Cicadas (the harvest-flies, seventeen-
year locusts, and the like) make sounds
that may sometimes be heard by us for
a mile or more. The ti'ansmitting
apparatus in this case is of still another
type. There is a pair of transmitting
diaphragms on the abdomen at about
the same place as the receiving dia-
phragms of the short-horned grass-
hoppers. A tendon and muscle is
attached to this transmitting dia-
phragm and by means of these it is
pulled in and then suddenly released.
As it snaps back, it makes a click. I
have here a little tin affair that lec-
turers often use to signal for a new
lantern shde. It is sometimes mis-
called a "cricket" but it should be
called a "cicada." The piece of tin is
bent somewhat and, as I push, it
bends the other way with a "click"
( — ). Then, when I let go, it snaps
back and makes another "click" ( — ).
The cicada does this so rapidly that the
clicks merge one into another so as to
make a sort of a buzz or a roar. The
best I can do is something like this
( — ) . It might be mentioned , inciden-
tally, and in accord with the Greek
poet, that onty the male cicadas make
this sound.



INSECT SOrXDS



2(J9



It is altotictlicr likch' lliat cicadas
would not ^o to all this troul)lc in
pi'odiiein^- soiuuls if other cicadas
could not luwr tluMii, hut I do not know
what their rccnnving apparatus, if
they have one, is like.

It is said that mosquitoes receive
sounds hv means of their antennae in a
very intcn-estins; way. We all know^ to
our sorrow the hum made by a mos-
quito. It is the hum made by a female
mosquito that is of most interest to
human l)eings because only the female
bites. Now% the antennae of all mos-
quitoes are feather-like or plumed
antennas, but especially so in the case
of the males. It is said that the hairs
which make up these plumes can be
set into rapid vibration by sounding
on a violin the same note that is made
by the female mosquito. I have not
seen this happen myself but I hope to
try it out this summer. It is probabh'
true, because we know that a tuning
fork or a piano string can be set into
vibration by sounding the note for
W' hich it is tuned. If the hairs on a male
mosquito's antennae are tuned to
vibrate at a note corresponding to the
female's hum, he can doubtless feel the
vibrations and so hear the hum just as
we feel vibrations of our ear-drum
and call those sensations hearing. (In
that case the mosquito does employ
antennae in its receiving apparatus but
there seems to be nothing electrical
about it nor anything that corresponds
to radio.) Far be it from me to suggest
that there is am^ connection betw^een
the facts that female mosquitoes are
not voiceless and do bite.

Although there is much more that
could be said about the transmission
and reception of sounds by insects,
there is nothing that is much more
definite than what I have told you.
Do ants and other insects actuallv



c( )ni mini icatc by means of sounds which
we cannot hear? No one knows but
sonic of us are trying to find out.

II

Probably the first definite sounds
made b}^ land-animals on this earth
were made by insects. Before ever
birds sang or even frogs croaked, in-
sects had developed a chitinous cover-
ing, the segments of which, rubbing
together, produced sound-waves.
Whether these sound-waves were audi-
ble in the sense that there were
organisms with nervous mechanisms
attuned to them might be the sub-
ject of an interesting speculation.
Crickets and katj^dids belong to the
order Orthoptera, and orthopteroid
insects were abundant in the Car-
boniferous period. In the fields and
forests of those days, or possibly earlier,
w^as started "the poetry of earth" that
"is never dead."

Judged by human ears, the best
insect-musicians of today belong to
rather primitive orders. The more
advanced groups, such as ants, bees,
wasps, flies, and butterflies, make no
sounds that we can hear or else, at
most, what seem to us to be nothing
more than faint squeaks, buzzes, hums,
or clicks. However, it is entirely prob-
able — indeed, practical!}^ certain — that
insect-sounds are not made for the
purpose of being heard by human ears.
Whether the insects themselves hear
these sounds is the important question
and one that has not been — possibly
cannot be — determined beyond all
doubt.

In this connection it should be re-
membered that, in man's affairs at
least, many sounds are made without
intention and even contrary to desire —
for examples, sneezing and snoring.
No part of the success of a certain



210



NATURAL HISTORY



popular kind of automobile is due to
the various and often loud noises
emitted by the machine in action.
Using an illustration more applicable
to the present subject, the armor of the
knights of old creaked and rattled as
they moved. Their fellows were able
to hear these sounds and reacted to
them. A i-ough spot in a particular
joint increased the sound made by the
moving of that joint. Now, if the
armor-maker purposely designed these
joints to creak or if the wearer pur-
posely creaked his armor, even if for
no other motive than to tickle his
pride (as has been the case with wearers
of squeaking shoes), then the creaking
of the joint had a significance analogous
to that usually claimed for certain
sounds made by insects — there w^as an
adaptation of structure to sound-
production. But, considering now the
sounds made by insects, if they are
merely incidental to friction between
parts of the body, analogous to uninten-
tional squeaks and rattles of knightly
armor, then those sounds have no bio-
logical significance, except as they may
betray the insect to its enemies.

Man has made many guesses as to
the significance of insect sounds, but
there are two points in this and similar
connections to be kept ever and
strongly in mind. One is that in
science a good guess is very useful as a
starting point but exceedingly harm-
ful if, forgetting that it is after all
only a guess, we accept it as a proved
fact. The second point is that it is
dangerous to judge the actions of
lower animals by human standards.
Was it not Paul who said that, when
he was a child, he thought and acted as
a child but, when he became a man, he
put away childish things? Well, a man
is much farther removed from the
lower animals than he is from a child



and, except in slang, he is not and
never was a bug. Bugs were not even
in his ancestral line.

There is much joy to be had in
giving free rein to our imagination and,
on the other hand, man prides himself
on being "practical," meaning that
everything must be of some use or be
abandoned. The combination of these
two human traits has resulted in most
ingenious stretches of human imagina-
tion to find the "practical" reason for
everything that we see or hear in this
world.

Prior to the Fifties of the last
century scores of books were written to
show that God was "practical" and
that everything was made by Him to
serve some definite, very useful pur-
pose. If no purpose could be imagined,
the failure was said to be due to the
fact that the ways of God were in-
scrutable and past finding out. Since
the Sixties, thousands of books and
papers have been written to show that
Natural Selection is eminently "prac-
tical" and that everything is forced bj^
it under penalty of extermination to
serve some definite and very useful
purpose. If no purpose can be imag-
ined, the failure is said to be due
solely to our present lack of knowledge
but the purpose is not past finding out.
We even have a name for this branch
of biology. It is ecology, the science
that gives a reason for everjrthing.

Lack of knowledge is, I am glad to
say, frequently a fact. It is the un-
known that makes biology more inter-
esting than arithmetic. Of the many
Latin mottoes I have seen — why do
they so often put good mottoes in
poor Latin? — one of the best for a
biologist is that which, being trans-
lated, reads: "We are ignorant; let
us work under this banner.' Let us
work under this banner but let us not



INSECT SOUNDS



211



dodge under it ov useil I'urllie jjurpuse
of tying together the pieces of a broken
theory.

As tt) the uni\-ersal praelifiiht}' of all
creation, I hope that the swinging
penduhini of human thought may
speedily bring us to a point where the
slogan ''Whatever is, is good" will be
changed to the more moderate one of
"Whatever is, is not bad." It is my
firm belief that many striking charac-
ters and characteristics of animals and
plants are of no use to their possessors
or to any other creature. As I have
said elsewhere, they seem to me to be
much like the figures in a kaleidoscope,
definite and doubtless due to some
internal mechanism but not serving
any special purpose.

However, we must be on our guard
against carrying any belief too far and
it would be absurd to say that no
special characteristic of any animal or
plant is useful to it; also, while some
insect sounds appear to have no bio-
logical significance, others do appear to
have a very decided significance. In
that case, we are brought to the
threshold of the real problem, really a
double problem: How and why has
the ability to make these particular
sounds arisen?

Most of the sounds made by verte-
brate animals are vocal, that is, they
are due to the combined action of
lungs and larynx. Insects have no
lungs, strictly speaking, and most of
the sounds which they make may, for
the want of a better term, be called
mechanical .

The simplest of these sounds is the
striking together of two parts of the
body. Certain bees, such as the domes-
ticated honey-bee, and certain flies,
such as the Syrphidse, make a shrill
noise when they are captured. For
years this sound was supposed to be a



vocal ()n(!. Instead of iiuigs, insects
have air-tubes ruiuiiu^ throughout
their bodi(>sand opening to the outside
as a series of small holes. These open-
ings are sometimes provided with mem-
branous flaps. All of these structures
were carefully dissected and beautifully
pictured by skilled anatomists, the
conclusion being that air, forced out
of the tubes, set the flaps into vibra-
tion and made the noise. This con-
clusion became firmly established by
ingenious experimentalists, who did
many things, including cutting off the
wings and noting that this did not
stop the sound. Then came one of
those troublesome fellows who upset
traditions. He pulled out the wings
instead of merely cutting them off and
then the sound stopped. He did other
things also and now we know that this
shrill note is caused simply by thr-
bases of the wings beating vigorously
against the body.

This sound has been very useful to
the proponents of the mimicry hypo-
thesis. According to theory, bees make
it to warn their captors that stinging is
about to start, a most sportsmanlike
trait; flies, on the other hand, make
this sound to fool their captors into
thinking that stinging is about to start,
and that trait is commendable only
on the grounds of self-preservation, foi-
flies have no sting. As a matter of fact ,
spiders are the flies' worst enemies and
spiders calmly tie up and kill bee and
fly alike, clearly paying no attention
to the noise and probably not being
able to hear it. Toads, frogs, and
lizards are the flies ' next worst enemies
but these predators finish their prey at
one gulp and the insects have no
chance to make a sound before they are
where feeling rather than hearing is
likely to tell the captor whether or not
it has swallowed a bee. Birds may be



212



NATURAL HISTORY



deceived — I do not know — but, despite
the fact that a large group of birds are
called flycatchers, they are not rela-
tively serious enemies of the Diptera
and there are birds that have a fondness
for bees — sting, warning sound, and all.
Therefore, it seems to me that this
shrill sound about which so much has
been written has no significance. It is
merely an incident to the extra vigor-
ous working of the wing-muscles under
the excitement of being captured.

There is a large and widely dis-
tributed group of grasshoppers the
members of which, unlike those of other
groups, have bright hind wings visible
only in flight. The males of this group
are much given to hovering over the
females, displaying these wings and
calling attention to the bright colors bj^
a rattling sound made by striking the
Avings together. At least, that is the
way it looks at first glance and it may
be true. And so this has become a
classic example of the theory of sexual
selection. Years ago I myself wrote a
perfectly orthodox paper on the "Ecol-
ogy of Insect Sounds" and used these
grasshoppers as the principal illustra-
tion. Since then I have spent many
hours in the hot sun watching the
lady in the case and I must say that, if
human lovers received as little response
to their serenades as do the courting
grasshoppers, most of them would
either give up music or remain
bachelors. Furthermore, the theory of
sexual selection requires that these
females have so much better ears than
ours that they are able to detect slight
differences in either the tone or the
intensity of a male's rattle. Of this
there is not a single bit of real evidence
and, in fact, most of the recent work
on the audition of insects tends to the
conclusion that, if they are not actually
deaf, they certainly pay but little atten-



tion to sounds within ovn- audible range.
It seems quite possible that this court-
ship music has no significance other
than an incidental hitting together of
the wings as the male hovers to get the
scent of a female hidden in the grass,
for we know that insects have very keen
olfactory powers but relatively poor
vision.

What I have seen happen is that,
when such a male comes back to eaith
and approaches the female, he nerv-
ously twitches his long hind legs up and
down. This brings me to a second class
of insect sounds, those made by friction
rather than beating.

Most insect sounds are made in this
way. Although the twitching legs of
which I have just spoken caused no
sound that I could hear, certain grass-
hoppers, belonging to a related group
but not having bright hind wings,
do make a sound audible to us when
the hind legs rub against the body.

The most familiar example of insect
sounds made by friction is the chirping
of crickets. Now, only the males do
this. Chirping is distinctly a secondary
sexual character, the stock explanation
of which is that it is a mating call
developed by sexual selection. The
adult life of a male cricket lasts a
month or so and he chirps most of the
time but he spends little of that time
in mating. Why does he chirp when
there is no female around? Possibly
hoping that one will come; I do not
know. When he has mated, his sexual
life is done but he keeps on chirping to
his dying day. I do not know why;
possibly to pass the time. I do know
this, however, and my knowledge is
based on the breeding of literally thou-
sands of crickets while I was using them
in a study of heredity : a female cricket
pays but little attention to a chirping
male. She may wave her antennae in



INSECT SOUNDS



213



liis direction hut so will she wIumi he is
not chirpinti and so will she at a stick
or a stone.

One of the most remarkable shall
I say — ''adaptations" among insects
for the pi'odiiction of sound by friction
is possessed by the grub of a beetle.
A pair of legs is grotesquely modified
and the insect rubs them against a sort
of a wash-board affair on its body.
This has been as good as a cross-word
puzzle for those who hunt for purpose
in ever^i;hing. The creature is imma-
ture and so is not looking for a mate.
It lives concealed in rotten wood, so we
have ti'ouble in believing that it keeps
on making the sound to fool unseen
enemies that do not see it into believing
that there is something dangerous,
instead of a nice fat grub, in that piece
of wood. One guess, soberly" made, is
that the sound is to notify brothers and
sisters of its presence so that they will not
eat too close to its preempted property.

When we can explain the purpose of
a man's snoring or of the rattling of a
Ford car, we may know why this beetle
grub rasps. Having slept with a man
that snored and having driven a Ford,
I believe that the sounds in question
are unintentional and quite incidental
to the structure of the man and of the
machine. May not the same be true
of the beetle grub?

Ph^^sicists tell us that the intensity
of a sound varies as the square of the
number of vibrations per second (that
is, the pitch) and also as the square
of the amplitude of these vibrations.



Xow, insects are small, weak creatures,
and the amplitude of any soinid-waves
made by them is therefore necessai'iiy
small. Consecjuently, an insect .sound