Among insects, sounds are produced in many ways, and for various reasons.
A species of ant which makes its nest on the under side of leaves produces
a noise by striking the leaf with its head in a series of spasmodic taps,
and another ant is also very interesting as regards its sound-producing
habit. "Individuals of this species are sometimes spread over a surface of
two square yards, many out of sight of the others; yet the tapping is set
up at the same moment, continued exactly the same space of time, and
stopped at the same instant. After the lapse of a few seconds, all
recommence simultaneously. The interval is always approximately of the
same duration, and each ant does not beat synchronously with every other
ant, but only like those in the same group, so the independent tappings
play a sort of tune, each group alike in time, but the tapping of the
whole mass beginning and ending at the same instant. This is doubtless a
means of communication."
The organ of hearing in insects is still to be discovered in many forms,
but in katydids it is situated on the middle of the fore-legs; in
butterflies on the sides of the thorax, while the tip of the horns or
antennae of many insects is considered to be the seat of this function. In
all it is little more than a cavity, over which a skin is stretched like a
drum-head, which thus reacts to the vibration. This seems to be very often
"tuned," as it were, to the sounds made by the particular species in which
it is found. A cricket will at times be unaffected by any sound, however
loud, while at the slightest "screek" or chirp of its own species, no
matter how faint, it will start its own little tune in all excitement.
The songs of the cicadas are noted all over the world. Darwin heard them
while anchored half a mile off the South American coast, and a giant
species of that country is said to produce a noise as loud as the whistle
of a locomotive. Only the males sing, the females being dumb, thus giving
rise to the well-known Grecian couplet:
"Happy the cicadas' lives,
For they all have voiceless wives."
Anyone who has entered a wood where thousands of the seventeen-year
cicadas were hatching has never forgotten it. A threshing machine, or a
gigantic frog chorus, is a fair comparison, and when a branch loaded with
these insects is shaken, the sound rises to a shrill screech or scream.
This noise is supposed--in fact is definitely known--to attract the female
insect, and although there may be in it some tender notes which we fail to
distinguish, yet let us hope that the absence of any highly organised
auditory organ may result in reducing the effect of a steam-engine whistle
to an agreeable whisper! It is thought that the vibrations are felt rather
than heard, in the sense that we use the word "hear"; if one has ever had
a cicada _zizz_ in one's hand, the electrical shocks which seem to go up
the arm help the belief in this idea. To many of us the song of the
cicada--softened by distance--will ever be pleasant on account of its
associations. When one attempts to picture a hot August day in a hay-field
or along a dusty road, the drowsy _zee-ing_ of this insect, growing louder
and more accelerated and then as gradually dying away, is a focus for the
mind's eye, around which the other details instantly group themselves.
The apparatus for producing this sound is one of the most complex in all
the animal kingdom. In brief, it consists of two external doors, capable
of being partly opened, and three internal membranes, to one of which is
attached a vibrating muscle, which, put in motion, sets all the others
vibrating in unison.
We attach a great deal of importance to the fact of being educated to the
appreciation of the highest class of music. We applaud our Paderewski, and
year after year are awed and delighted with wonderful operatic music, yet
seldom is the _limitation_ of human perception of musical sounds
considered.
If we wish to appreciate the limits within which the human ear is capable
of distinguishing sounds, we should sit down in a meadow, some hot
midsummer day, and listen to the subdued running murmur of the myriads of
insects. Many are very distinct to our ears and we have little trouble in
tracing them to their source. Such are crickets and grasshoppers, which
fiddle and rasp their roughened hind legs against their wings. Some
butterflies have the power of making a sharp crackling sound by means of
hooks on the wings. The katydid, so annoying to some in its persistent
ditty, so full of reminiscences to others of us, is a large, green,
fiddling grasshopper.
Another sound which is typical of summer is the hum of insects' wings,
sometimes, as near a beehive, rising to a subdued roar. The higher,
thinner song of the mosquito's wings is unfortunately familiar to us, and
we must remember that the varying tone of the hum of each species may be
of the greatest importance to it as a means of recognition. Many beetles
have a projecting horn on the under side of the body which they can snap
against another projection, and by this means call their lady-loves,
literally "playing the bones" in their minstrel serenade.
Although we can readily distinguish the sounds which these insects
produce, yet there are hundreds of small creatures, and even large ones,
which are provided with organs of hearing, but whose language is too fine
for our coarse perceptions. The vibrations--chirps, hums, and clicks--can
be recorded on delicate instruments, but, just as there are shades and
colours at both ends of the spectrum which our eyes cannot perceive, so
there are tones running we know not how far beyond the scale limits which
affect our ears. Some creatures utter noises so shrill, so sharp, that it
pains our ears to listen to them, and these are probably on the borderland
of our sound-world.
Pipe, little minstrels of the waning year,
In gentle concert pipe!
Pipe the warm noons; the mellow harvest near;
The apples dropping ripe;
The sweet sad hush on Nature's gladness laid;
The sounds through silence heard!
Pipe tenderly the passing of the year.
Harriet Mcewen Kimball.
I love to hear thine earnest voice,
Wherever thou art hid,
Thou testy little dogmatist,
Thou pretty Katydid!
Thou mindest me of gentlefolks,--
Old gentlefolks are they,--
Thou say'st an undisputed thing
In such a solemn way.
Oliver Wendell Holmes.
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