The ears of the Gryllidae have not been so well investigated as those of the Locustidae, but are apparently of a much less perfect nature. No orifice for the admission of air other than that of the prothoracic stigma has been detected, except in Gryllotalpa. On the other hand, it is said[[260]] that in addition to the tibial organs another pair of tympana exists, and is seated on the second abdominal segment in a position analogous to that occupied by the ear on the first segment of Acridiidae.
The musical powers of the crickets are remarkable, and are familiar to all in Europe, as the performance of the house-cricket gives a fair idea of them. Some of the Insects of the family are able to make a very piercing noise, the note of Brachytrypes megacephalus having been heard, it is said, at a distance of a mile from where it was being produced. The mode of production is the same as in the Locustidae, rapid vibration of the tegmina causing the edge of one of them to act on the file of the other.
The mole-cricket, Gryllotalpa vulgaris—the Werre of the Germans, Courtilière of the French—is placed with a few allies in a special group, Gryllotalpides, characterised by the dilated front legs, which are admirably adapted for working underground. Like the mole, this Insect has a subterranean existence. It travels in burrows of its own formation, and it also forms beneath the surface a habitation for its eggs and family. Its habits have been alluded to by Gilbert White,[[261]] who tells us that "a gardener at a house where I was on a visit, happening to be mowing, on the 6th of May, by the side of a canal, his scythe struck too deep, pared off a large piece of turf, and laid open to view a curious scene of domestic economy: there were many caverns and winding passages leading to a kind of chamber, neatly smoothed and rounded, and about the size of a moderate snuff-box. Within this secret nursery were deposited near a hundred eggs of a dirty yellow colour, and enveloped in a tough skin, but too lately excluded to contain any rudiments of young, being full of a viscous substance. The eggs lay but shallow, and within the influence of the sun, just under a little heap of fresh moved mould like that which is raised by ants."
Fig. 206.—Front leg of the mole-cricket. A, outer; B, inner aspect: e, ear-slit.
The front legs are remarkable structures (Fig. 206), being beautifully adapted for burrowing; the tibiae and tarsi are arranged so as to act as shears when it may be necessary to sever a root. The shear-like action of the tarsus and tibia is very remarkable; the first and second joints of the former are furnished with hard processes, which, when the tarsus is moved, pass over the edges of the tibial teeth in such a way as to be more effective than a pair of shears. In consequence of its habit of cutting roots, the mole-cricket causes some damage where it is abundant. It is now a rare Insect in England, and is almost confined to the southern counties, but in the gardens of Central and Southern Europe it is very abundant. Its French name courtilière is supposed to be a corruption of the Latin curtilla. Its fondness for the neighbourhood of water is well known. De Saussure says that in order to secure specimens it is only necessary to throw water on the paths between the flower-beds of gardens and to cover the wetted places with pieces of board; in the morning some of these Insects are almost sure to be found under the boards disporting themselves in the mud. The Gryllotalpae swim admirably by aid of their broad front legs.
Ears exist in the mole-cricket, and are situate on the front leg below the knee, as in other Gryllidae, although it seems strange that a leg so profoundly modified for digging and excavating as is that of the mole-cricket should be provided with an ear. In Gryllotalpa the ear is concealed and protected by being placed in a deep slit or fold of the surface, and this depression is all that can be seen by examination of the exterior (Fig. 206, e). In the allied genus Scapteriscus the tympanal membrane is, however, destitute of special protection, being completely exposed on the surface of the leg.
Although the tegmina or upper wings in Gryllotalpa are of small size, yet the true wings are much more ample; they are of delicate texture and traversed by many nearly straight radii, so that they close up in the most complete manner, and form the two long delicate, flexible processes that in the state of repose may be seen projecting not only beyond the tegmina, but actually surpassing the extremity of the body hanging down behind it, and looking like a second pair of cerci.
The mole-cricket is believed to be chiefly carnivorous in its diet, though, like many other Orthoptera, it can accommodate its appetite to parts of the vegetable as well as of the animal kingdom. The Insect is capable of emitting a sound consisting of a dull jarring note, somewhat like that of the goat-sucker. For this purpose the tegmina of the males are provided with an apparatus of the nature we have already described, but which is very much smaller and less elaborate than it is in the true crickets.
