For an example of the Gimlet we may take the ovipositor of the Sirex, an insect which I believe has no popular name. It is coloured much after the same manner as the hornet, and is often mistaken for that insect by those who are not versed in entomology. And, as its long and straight ovipositor is generally taken for a hornet’s sting, the insect assumes a double terror to the ignorant.
Now, the real fact is, that in its larval stage of existence the Sirex feeds upon the wood of the fir-tree—a diet which, to our ideas, is about as unsatisfactory as can well be imagined. In order that the young Sirex may be within reach of food, the egg must be introduced deeply into the body of the tree, and, for the egg to be so received, a channel must be cut for it.
This is done by means of the marvellously formed ovipositor. Many admirable descriptions have been given of the head of this instrument and its boring powers, but I am not aware that any one has noticed the secondary cutting blades that are set along the shaft of the principal borer, and which answer exactly the same purpose as the spiral cutting edge of the gimlet or auger.
Not being desirous of repeating my own observations in different words, I transfer to these pages a short account of the ovipositor of the Sirex, as examined by me when writing my work on British Insects, entitled “Insects at Home,” and published by Messrs. Longmans and Co.:—
“I very strongly recommend any of my readers who may obtain a female Sirex to disengage the actual borer from its two-bladed sheath, and examine it with the aid of a microscope. A half-inch object-glass will give quite a sufficient power.”
“It is straight, stiff, and elastic, as if made of steel, and, if bent, will spring back to its proper form with the elasticity of a Toledo rapier.
“But the borer possesses an auxiliary cutting apparatus which places it far above the rymer in point of efficacy. Even with an ordinary magnifying lens, it is easy to see that the end of the borer is developed into a sharp head, very much resembling that of a boarding-pike, and that the outline of the shaft is broken into a series of notches.
“The half-inch glass, however, discloses a marvellous example of mechanical excellence. The head of the borer is then seen to be armed with long, sharp teeth, slightly curved inwards, and acting just as does the carpenter’s ordinary centrebit.
“So much for the head of the borer: we will now turn to the shaft.