True Tales of the Insects

the process of extrication is complete. Pale and colourless when first having drawn itself out of this skin, the full-born larva is nevertheless at once capable of walking firmly on its legs, and even hops with agility, and an hour seldom elapses after the moult takes place ere its natural dark grey colouring is acquired.

However thin and delicate this pellicle discarded by the little animal on issuing from the egg may be, it doubtless affords much protection in the struggles of birth, and Riley points out the interesting fact that while, as we have just seen, it is shed within a very few minutes of the time when the animal reaches the free air, it is rarely shed if, from some cause or other, there is failure to get out of the soil, even though the young may be striving for days to effect an escape.

Post-embryonic Development.

Let us trace a migratory locust, Schistocerca peregrina, through its post-embryonic development; following Brongniart. Immediately on leaving the egg the young locust changes its skin, and is then of a green colour, but quickly becomes brown, and in twelve hours is black. Already at this early age the gregarious habit proclaims itself. In six days the individual experiences a second moult, after which it is black, mixed with

I02 TRUE TALES OF THE INSECTS.

white, and with a rosy streak on each side of the hind body. Generally six or eight days later the third ecdysis takes place; the general tint being the same, but the rose colour becomes more distinct. After eight days the fourth moult occurs; when the creature should be considered no longer a larva, but a nymph, for it has the first rudiments of wings; the position of the markings is the same, but the rose colour is altered to a citron yellow, and the line of the spiracles is marked with white. In ten days another moult is undergone, there is considerable increase in size, the yellow is brighter, and the prothorax more definitely speckled with white. In fifteen or twenty days the sixth ecdysis occurs, and the locust enters the perfect state. The large tegmina now present are marked with black, and the surface generally is rosy and bluish. Such is the colour in Algeria; yet sometimes the insects arrive from the South in the French colony reddish or yellowish in colour, those of the latter tint being, it is believed, older specimens of the red kind. We may recall an analogous series of colour-changes in the course of the of theindividual development of some Phasmidse— Phyllium group. The fact of these changes of colour in Orthoptera during metamorphoses, and even after they have become adult, is important, not only from a physiological point of view, but as helping towards the determination

of the number of species and the geographical distribution of the migratory locusts.

On an average, the Rocky Mountain Locust requires about seven weeks, from the time of hatching, to pass through its stages of growth; and the perfect form is attained through a series of five moults.

Apart from the colorational, and more minute structural changes which take place with each moult, the most striking change in the course of development is the orrowth of the wino-s. We examine the first instar of Calopteims spretus, the young locust just emerged from the eesf and colourless. In the second instar the chief difference is the development of colour; in the third there is plainly a slight development of the future organs of flight. After the third moult there is a great change; the instar then disclosed — the fourth—has undergone a considerable change in the wing-rudiments or wing-pads, which have become free and detached, the second pair being the larger, and outside the other pair. The fifth instar differs little, except in the increased size of the wing-pads. At the fifth and last moult the instar is the perfect insect, with full free wings, the thorax flattened, the colour dift'erent. The most pronounced changes, it will be observed, occurred at the third and fifth skin-sheddings, after each of which considerable difference in the form of the insect was presented.

ro4 TRUE TALES OF THE INSECTS.

Before each ecdysis the locust stops feeding for a while and remains motionless. The first three or larval skins are almost invariably shed on or near the ground, the young crowding together in some sheltered nook; for the last two or pupal moults they seem to prefer to fasten to some elevated object. Immediately after the operation the bod)- is soft and colourless, as it was on leaving the ^'g%. Obviously these moults are most critical periods, and to the winged—-is the mostthe last moult—from pupa critical, the most difficult of all. Clutchinof a orrass-stem, or whatever be the chosen object, securely with its hind feet, which are drawn up under the body; the head downwards, if in the favourite position; motionless, with antennae drawn down over the face, the whole attitude betokening the pupa awaits the helplessness,—thus swelling, and the ultimate splitting of the skin, when the struggle ensues to find release. Having succeeded at last in drawing itself out of its old " misfit," it, with unsteady gait, turns round and clambers up the side of the shrunken cast-off coat, and there rests while the body hardens, the crooked limbs straighten, and the wings dry, unfold, and expand, like the petals of some opening flower. The pale colours appertaining to moulting gradually give way to the natural tints, and a fresh bright locust eventually starts on a new career. Ravenous from long fast, by-and-by it joins its voracious

comrades, and makes initial essay of its new jaws. During the helplessness that belongs to these crises, the unfortunate creature falls a victim to many enemies which otherwise would not molest it, and not unfrequently to the voracity of the more active individuals of its own kind.

CHAPTER YI.

LOCUSTS AND GRASSHOPPERS (acridiid.e)— Continued.

Locusts.

Only a few of the various kinds of grasshoppers belonging to this family Acridiidai—of which nearly two correctly denomi-thousand species are known—can be nated locusts. A locust is a species of grasshopper that occasionally becomes very destructive, and that moves about in swarms to seek fresh food. Some Acridiidae greatly increase in numbers locally, and become very often for one or two seasons onlydestructive—very and still more rarely migrate from place to place, and are then called locusts. The true migratory locusts are species that have the migratory instinct or disposition strongly developed, and that move over considerable distances in swarms, and inflict serious injuries. Of less than a dozen, inthese there are but few species-we hear of their swarms in many partsfact—although of the world.

Perhaps the most important and widely distributed of them is Pachytybis cinerasccns, which has extended its invasions over a great part of the Eastern hemisphere, from China to the Atlantic Ocean. It exists in many places in the Orient and the Asiatic Archipelago, and even in New Zealand, and is the commoner European migratory locust; its congener, P. migra-torius, being much more restricted in distribution. P. {ccdaleiis) inar-inorat2is has almost as wide a distribution in the Eastern hemisphere as P. cincrasccns, but is more exclusively tropical. These locusts

Fig. 21. Proscopia imvqnaHs, belong to the Oedipodides. This which hears a great general tribe does not include all the resemblance to a Stick Insect. species of migratory locusts of the Old World; Schistoccrca peregrina belongs to the tribe Acridiides. This handsome locust has a wide distribution. It is the chief species in North Africa, as in North-west India, and is probably the locust in Exodus. With this sole exception, the species of the genus Schistocerca are confined to the New World. Schistocerca aincricana is migratory to a small extent in the United States; and other species are migratory in South America. The

io8 TRUE TALES OF THE INSECTS.

genus Caloptenus also belongs to Acridiides. Several species of this genus are injurious in North America, but the migratory habit and great destructive power belong essentially to the Rocky Mountain Locust, the too famous Calopienus spretus. While none other compares with it there in the vastness of its movements, or the injury which it inflicts, it, nevertheless, is a comparatively small, inconspicuous species, its slender brownish body seldom exceeding an inch and a quarter in length. We ascertain plainly from the above facts that the migratory species of Acridiidae are not limited to any one genus or group of the family; and it is evident, therefore, we must look to something else than such anatomical characteristics or differences as distinguish the groups for the cause of the migratory instinct.

We should bear in mind this equally well established fact that locusts of the migratory species exist in countries without giving rise to swarms, or causing serious injuries; thus P. cinerascens is always present in different localities in Belorium, and does not Cfive rise to swarms.

Occasionally individuals of these migratory species penetrate to our shores. In 1869 specimens of Schistoccrca peregrina occurred in various parts of the country, having in all probability arrived by crossing the German Ocean, and P. cinerascens and P. migratorins have been met with; but Britain is now exempt from the ravages of locusts.

Migration of Locusts.

Insignificant individually, but mighty collectively, the migratory locusts fall upon a country liable to their visitations like a blight, for they appear suddenly on a spot in huge swarms, which, in the space of a few hours, clear off all the vegetation that can be eaten, leaving brown and bare that which all was green and flourishing. It is difficult for those who have not witnessed a serious invasion to fully conceive, or appreciate it. So great the proportions of the scourge, so vast their multitudes, their flight may be likened to a vast body of fleecy clouds, or, still more correctly, to an immense snowstorm, often extending from near the ground to a height that baffles the keenest eye to distinguish the insects in the upper stratum. It is a vast mass of animated specks glittering against the sun. On the horizon, they often appear as a heavy black cloud. So densely packed the brood, they occasionally even darken the air, intercepting the sun's rays for hours, and casting a checkered shade over the earth. Carruthers, in Nature, estimates a great flight of locusts that passed over the s.s. Golconda, when off the Great Hanish Islands in the Red Sea, in November 1889, at over two thousand square miles in extent; the number of insects he calculates to have been 24,420 billions;

no TRUE TALES OF THE INSECTS.

and the weight of the mass 42,580 mihions of tons, each locust weighing one-sixteenth of an ounce; and the ship of six thousand tons burden, he adds, must have made seven milHon voyages to carry this great host, even if packed together 1 1 i times more closely than they were flying. Another, apparently a stronger, flight was seen going in the same direction next day. Other testimony goes to prove that such an estimate may be no exaggeration. According to official accounts of locusts in Cyprus, no fewer than 1600 million egg-cases were collected and made away with in 1881, up to the end of October; and by the end of the season the weight of the eggs collected and destroyed amounted to over 1 300 tons. From one part of the country to another the great hordes sweep, in search of pastures new, and leave ruin and devastation in their wake. The earth is entirely deprived of her green mantle, no green thing is left for beast or man. Famine is only a too probable consequence, and pestilence may follow from the decomposition of the bodies of the dead insects. The latter result is said on some occasions to have occurred from swarms falling into the sea, and being drowned, and being afterwards thrown upon the shore by the waves. Sometimes bodies of young locusts plunge into a stream and are entrapped there, the whole swarm being swamped in the river, there being no current to carry