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 antennÆ 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:

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.