The Grasshopper, so remarkable both for the length and thickness of her hinder thighs and for her ovipositor, the sabre or dibble which plants her eggs, is one of the chief performers in the entomological concert. Indeed, if we except the Cicada, who is often confused with her, she is responsible for the greater part of the noise. Only one of the Orthoptera surpasses her; and that is [[259]]the Cricket, her near neighbour. Let us first listen to the White-faced Decticus.
The performance begins with a hard, sharp, almost metallic sound, very like that emitted by the Thrush keeping a sharp look-out while he stuffs himself with olives. It consists of a series of isolated notes, tick-tick, with a longish pause between them. Then, with a gradual crescendo, the song develops into a rapid clicking in which the fundamental tick-tick is accompanied by a continuous droning bass. At the end the crescendo becomes so loud that the metallic note disappears and the sound is transformed into a mere rustle, a frrrr-frrrr-frrrr of the greatest rapidity.
The performer goes on like this for hours, with alternating strophes and rests. In calm weather, the song, at its height, can be heard twenty steps away. That is no great distance. The noise made by the Cicada and the Cricket carries much farther.
How are the strains produced? The books which I am able to consult leave me perplexed. They tell me of the “mirror,” a thin, quivering membrane which glistens like a blade of mica; but how is this membrane made to vibrate? That is what they [[260]]either do not tell us or else tell us very vaguely and inaccurately, talking of a friction of the wing-cases, mutual rubbing of the nervures; and that is all.
I should like a more lucid explanation, for a Grasshopper’s musical-box, I feel certain in advance, must have an exact mechanism of its own. Let us therefore look into the matter, even though we have to repeat observations already perhaps made by others, but unknown to a recluse like myself, whose whole library consists of a few old odd volumes.
The Decticus’ wing-cases widen at the base and form on the insect’s back a flat sunken surface shaped like an elongated triangle. This is the sounding-board. Here the left wing-case folds over the right and, when at rest, completely covers the latter’s musical apparatus. The most distinct and, from time immemorial, the best-known part of it is the mirror, thus called because of the shininess of its thin oval membrane, set in the frame of a nervure. It is very like the skin of a drum, of an exquisitely delicate tympanum, with this difference, that it sounds without being tapped. Nothing touches the mirror when the Decticus sings. Its vibrations [[261]]are imparted to it after starting elsewhere. And how? I will tell you.
Its edging is prolonged at the inner angle of the base by a wide, blunt tooth, furnished at the end with a more prominent and powerful fold than the other nervures distributed here and there. I will call this fold the friction-nervure. This is the starting-point of the concussion that makes the mirror resound. The evidence will appear when the remainder of the apparatus is known.
This remainder, the motor mechanism, is on the left wing-case, covering the other with its flat edge. Outside, there is nothing remarkable, unless it be—and even then one has to be on the look-out for it—a sort of slightly slanting, transversal pad, which might very easily be taken for a thicker nervure than the others.
But examine the lower surface through the magnifying-glass. The pad is much more than an ordinary nervure. It is an instrument of the highest precision, a magnificent indented bow, marvellously regular on its diminutive scale. Never did human industry, when cutting metal for the most delicate clockwork mechanism, achieve such perfection. Its shape is that of a curved spindle. [[262]]From one end to the other there have been cut across this bow about eighty triangular teeth, which are very even and are of some hard, durable material, dark-brown in colour.
The use of this mechanical gem is obvious. If we take a dead Decticus and lift the flat rim of the two wing-cases slightly in order to place them in the position which they occupy when sounding, we see the bow fitting its indentations to the terminal nervure which I have called the friction-nervure; we follow the line of teeth which, from end to end of the row, never swerve from the points to be set in motion; and, if the operation be done at all dexterously, the dead insect sings, that is to say, strikes a few of its clicking notes.