Through a pocket lens

by Henry Scherren

When the insect is about to deposit her eggs, she selects a spot where the soil is light, and bending the ovipositor nearly at a right angle to her body, thrusts it into the ground as far as possible. Then, by a muscular effort, the plates of the ovipositor are separated, and several eggs travel down the passage formed by the central pair of rods into the hole. This is repeated time after time, till the operation of egg-laying is completed. This takes place in the autumn, and the young emerge from the eggs in the spring. When they come out they are tiny copies of the adults; but they do not acquire wings till after several months. The ovipositor of the female appears after the second moult, and till this organ is developed no difference is apparent between the young insects.

The chief interest of the male insect lies in its wings, for the first pair (the teg´mina) are the organs with which it produces its ‘love-songs.’ Kirby comments on the fact that Lichtenstein, in the Linnaean Transactions (iv. 51), ‘draws attention to the eye-like area in the right wing-case of the males of this genus,’ adding that that author seemed ‘not to be aware that De Geer had noticed it before him, as a sexual character; and also, with good reason, supposed that it assists these animals in the sounds they produce.’

This is how De Geer (Mémoires, iii. 429) describes the sound-producing apparatus of the Great Green Grasshopper: ‘In our male grasshoppers, in that part of the right elytron which is folded horizontally over the trunk, there is a round plate of very fine transparent membrane, resembling a little mirror or piece of talc, of the tension of a drum. This membrane is surrounded by a strong and prominent nervure, and is concealed under the fold of the left elytron, which has also several prominent nervures answering to the margin of the membrane or ocellus. There is every reason to believe that the brisk movement with which the grasshopper rubs these nervures against each other produces a vibration in the membrane, augmenting the sound. The males in question sing continually in the hedges in the months of July and August, especially towards sunset, and part of the night. When any one approaches they immediately cease their “song.”’

It is probably unnecessary to do more than remark that the noises made by Insects do not correspond to the voices of the higher animals. ‘For no insect, like the larger animals, uses its mouth for utterance of any kind: in this respect they are all perfectly mute; and, though incessantly noisy, are everlastingly silent[26].’

Our plan with these wings is to first verify the fact of their bearing these talc-like spots, the serrated nervures on the right and the rudimentary file on the left elytron. The sound is produced by rubbing the base of the left elytron against that of the right. A recent author compares this insect to a fiddler, and says that the left tegmen is the bow and the right the fiddle.

The last point to examine is the ear. It seems strange to say that these insects have ears in their legs; but though some of the older entomologists regarded these structures in the tibiae of the first pair of legs as nothing more than resonators or sound-boards to intensify their chirping, there is no doubt that they are really organs of hearing. Much interesting information on this subject will be found in Sir John Lubbock’s Senses of Animals.

Fig. 40.—Tibial ear of Great Green Grasshopper.

These oval patches are plainly distinguishable by the unassisted eye, and correspond in function to the tympanum or drum of the human ear. The air-supply to the tibiae is distinct from that of the rest of the body, and is derived from a large orifice on each side of the first segment of the thorax. These orifices may be seen by removing the ‘hood.’ Indeed, they cannot escape observation. From these orifices an air-tube passes to each leg, dividing into two branches in the tibia and reuniting below the drums.

Dr. Sharp[27] says that ‘although the tibial ears of the Locus´tidae are very perfect organs, there is great difficulty in deciding on the exact nature of their functions. They would appear to be admirably adapted to determine the precise locality from which a sound proceeds ... for the legs can be moved in the freest manner in every direction, so as to bring the drum into the most direct line of the vibrations. But as to what kinds of vibrations may be perceived, and the manner in which they may be transmitted to the nerves, there is but little evidence.’