True Tales of the Insects
they are in the male of this insect. It would appear probable it has the power of producing two, if not more, distinct sounds. In habit it is exceedingly sedentary, and apparently seeks safety in its protective resemblance and its stridulation, rather than by any attempt at flight. Its wings indeed are totally unfit for movement, being quite rudimentary, and the posterior legs seem equally unadapted for this purpose; they are enormous in breadth, dilated more than in other AcridiidaD. When Methone walks, it does so by means of its four anterior legs alone, on which it moves raised up as if on stilts, when probably the hind pair drag useless along the ground. In repose these odd hind legs are pressed close to the sides of the body, and the tibiae are hid, the insect its colours being those of the desert sandsthen-resembling, so closely as to be mistaken for, a clod of earth. Among others modified to an extraordinary extent for their conditions of life, there is the curious Tj'achy-petra dn/o, another South African species. It lives among stones, and Trimen says it resembles with such precision the appearance of the stones that he had much difficulty to detect it. He noticed that in certain spots, often only a few square yards in extent, where the stones lying on the ground were darker, lighter, or more mottled than those generally prevalent, the
I40 TRUE TALES OF THE INSECTS.
individuals of the grasshopper varied similarly in colour in imitation of the stones. The differences found among individuals of the same species of desert Eremobiens are sometimes wonderfully great.
Two peculiar North American genera, Haldmanella and Brachystola, are known to represent this group in the New World. From its strange form and movements, B. magna has received the popular names of "buffalo-hopper" and "lubber-grasshopper." Almost equal in size to i\Iethone anderssoni, it is not, like that insect, in correspondence with arid spots. It inhabits verdant prairies in temperate regions; and is more or less smooth of body, and green in tint, and rests concealed during the day under tufts of grass. Sound-producing instruments it has none, though there may be vestiees or rudiments of these.
Our native Acridiidee belong chiefly to the genera Stenobothrus and Gomphocerus, whose musical instruments have been described. They are the little grasshoppers which are common in our fields, and well known to children for their saltatorial powers. The species of the genus Tettix are not uncommon. Besides these AcridiidcE, it will be remembered, three species of migratory locusts are occasionally met with in Britain.
CHAPTER VII.
GREEN GRASSHOPPERS (lOCUSTID^).
The family Locustidse contains none of the true locusts. From the Acridiid?e we have seen these insects can be readily distinguished by their very long, delicate antennae and four-jointed tarsi; and in other characters they differ essentially. Although as a rule provided with large wings, they have not the same power of flight as the Acridiidae; it is believed there are no air vesicles connected with the tracheal system; and to this may be due the fact that none of the Locustidae undertake those great migrations, so destructive to vegetation, that have rendered some of the foregoing family notorious. As a rule, they are less robust than Acridiidae, their ocelli are considerably less perfect, and the head is often produced in front into a curious cone-shaped projection, the use of which is totally unknown, as in a large number of Conocephalides. One of their most characteristic features is the ovipositor, which frequently exceeds the length of the body. Not present in the newly-hatched
Locustid, the organ becomes gradually developed, and the completed structure is formed by the apposition of no less than six rods or pieces.
Life Histories. Its mode of use is not always the same, some species depositing their eggs in the earth, and some place them
Fig. 24. Pterochroza ocellata, its tegmina resembling leaves.
in parts of plants. Light soil, easily pierced, is chosen, and the apparatus thrust to a considerable depth into
the ground. The British iMeconcuia variuni lays in the galls developed on oaks by the puncture of Cynips.
Fig. 25.—a cave-dweller (Dolickopada palpata). We find somewhat similar habits in North America, in Xiphidiuvi cnsifcruin, a very common Locustid in some of the States, the silvery napiform galls produced by a species of Cecidomyia on the stems of willows being selected for the reception of the eggs. The insect thrusts its ensate ovipositor in between the imbricated scales, and leaves the eggs completely concealed, the overlapping edges of the scales springing back to their original positions as soon as the ovipositor is withdrawn. Some of these Cecidomyia galls are more or less fusiform, with flat, closely applied scales, which are far less well adapted than the more spacious interstices of the globular galls for the eggs. Between the closely appressed scales of the spindle-shaped galls, many are so flattened as to be incapable of developing; but the Locustids appear to show no preference for the globular
galls. They seem, however, to prefer ovipositing, not in fresh galls, as might be supposed, but in blackened and weather-beaten specimens that have persisted through several seasons, probably because the scales are more easily forced apart.*
Since the imagines of X. ensiferuvi oviposit from the middle of August to September, and hatching is delayed until the following May or June, eight to nine months is therefore required for embryonic development, and the whole post-embryonic development must be passed through in three months. Development of the embryo begins in autumn, but a period of quiescence super-venes, due to cold weather.
Several of the congeners of X. ensiferuin lay their eggs in the pith of twigs. Fissures in twigs and stems of trees and shrubs are chosen by many for the purpose. The eggs of Microccntnis retinervis constantly attract attention on account of their large size, their remarkable regularity of arrangement, and exposed position. They are deposited in one or two rows overlapping each other, upon twigs or margins of leaves. They are laid in autumn, during the day occasionally, but usually at night, and become more swollen as they approach the hatching period in spring. In the early part of May hatching occurs, the young insect undergoing a moult during the process. By the time emergence is completed,
- Embryology of this insect, Wheeler, J. Morphol.^ viii. 1893.
it is a matter of wonder how the Microcentrum could so recently have been compressed into the comparatively-small shell beside it. After a few minutes the little beings essay their first leaps, and soon commence to eat with avidity. Including the moult in leaving the egg, they cast skins five times, acquiring wings at the fifth. Almost the first efforts of the liberated insect are directed to the task of eating up its out-grown and out-worn integument. Post-embryonic development takes about ten weeks. When first out of the pupal covering, the wings hang down on each side, limp and shapeless, but soon begin to dry and harden, and gradually are drawn into place, and assume their green colour.
Ears.
The Locustidse resemble the Acridiidae in the possession of special organs of hearing, or ears, but their situation is not the same as in Acridiidae. In Locustidse, in both sexes, a pair of ears usually occur near the proximal end of each tibia of the front pair of legs; a tympanum, or a slit or crack opening into a cavity in which the tympanum is placed, is seen on each side of the legs. The ears may be divided into two principal kinds, according to the state of the tympanum, which is either exposed, or hid by a prominence of the
integfument. That these orofans on the leg's of Locustidse are auditory organs has been ascertained beyond doubt. It is, in fact, only reasonable that insects provided with special sound-producing apparatus, as we shall presently see the Locustidae are, should also be furnished with specialized ears, A structure of a remarkable nature occurs in connection with the ears. At the posterior lateral angle of the prothorax, just over the insertion of the front leg, an open orifice is found; it is quite close to the prothoracic stigma, but is larger than it; it communicates with the one on the opposite side, and from them there extend processes along the anterior legs that narrow in passing the knee, and at last dilate in the tibiae, so as to form longitudinal vesicles, one of which is in proximity to each tympanum of the ear. This prothoracic orifice, which exists in the two sexes, among nymphs, and among larvae, and these leg-tracheae, do not communicate with the tracheal system. Why the acoustic organs should require a supply of air other than that which could be obtained through the ordinary tracheal system, remains to be determined. Although these tibial organs of Locustidae have certainly the function of hearing, there is great difficulty in deciding as to the exact kind of sounds to which they are sensitive. Nor is it even understood how the sounds are transmitted to the nerves.
Musical Organs and Music.
The Locustidre are famed for their musical powers. Among them, the stridulating apparatus, when present, is always situate on the base of the wing-covers. The left-hand tegmen has a roughened portion on the inner surface, serving as a file or bar, the right tegmen has a sharp edge on its inner margin; and by rubbing the base of one wing-cover upon the other, and vibrating them rapidly, a musical sound, or stridulation, is produced. The extent of the delicate vibrating membrane of the wings which is brought into action is small, and when the tegmina are very rudimentary in size, it is these fields indispensable for stridulation that are preserved. With but few exceptions, the males alone are provided with organs of stridulation; in the tribe Ephippigerides they exist in both sexes.
There is much variety in the structure. In this portion of the tegmina, the nervures not only differ in the male from those of the female, the arrangement of the nervures in the male is not symmetrical in the two tegmina. On the right tegmen is usually a small plate, or space, formed by a slender, tightly stretched, hyaline membrane, which, being put into vibration, probably increases the sound. In our large Green Grasshopper, Locusta viridissinia, though the musical organs are by
no means of a highly specialized character, each tegmen appears to act as a sounding-board.
Although in a large number of instances amply winged, the Locustid^e seem generally of a somewhat sedentary nature, availing themselves little of the wings for flight, using them rather as a kind of parachute, in descending from the trees to the ground. Moreover, they are chieHy nocturnal in their habits, though not entirely so. " These are the merry choristers," says Riley, speaking of American forms, " that make our woods and valleys ring with their pleasant songs during the evenings of late summer and early fall." The songs of the different species are very varied; indeed, each different species its peculiar note;may ordinarily be distinguished by but the study not infrequently presents some difficul-ties. Locusta viridissima produces a shrill stridulation, and sometimes chirps a little in the day. Bates tells us of one of these green grasshoppers, on the Lower Amazons, whose notes were the loudest and most extraordinary of any orthopterous insect he ever heard. Its native name, Tanana, is in allusion to its music. The natives keep it in small wicker cages for the sake of its sonor. The loud note of one could be heard from one end of the village to the other.