LOCUSTS.
During the past century considerable study has been centred upon the life and habits of the locust, mainly from the desire to seek its subjugation and destruction, and, whilst much general biological information has been written upon the subject, there are things which we do not yet know about this insect or its habits. We do not know what precise influences cause their migration, nor do we know what is the exact length of life of the locust or its breeding power, or the precise locality in any country which may be defined as its permanent abode. Locusts are classified under the order of orthopterous insects of the family Acrydiidae, and are very closely related to grasshoppers.
There are a large number of species, the differentiating features being more or less the form and sculpture of protorax, the size of the head, the length and size of the prosternal spine, the comparative length and size of the hind thighs and shanks, the amount and arrangement of the tegmina mottlings, the comparative length of wings, and the general build of the entire insect, which may be robust or fairly slender.
A general description of the distinctive physical features of migratory locusts might be given as a strong, wild-looking head, a strong collar inside which the neck moves, powerful and peculiarly-formed legs attached to a short, strong, square trunk or thorax, four wings, two antennae or feelers, six legs, and a long segmentary abdomen. The ground colour of the locust is generally brownish, straw, or red, but its colour varies somewhat according to the particular season of the year or some other peculiar circumstance, but nothing certain is known as to what influences the shade of colour. Mere ground colour is immaterial and does not signify a new species.
Besides having a pair of compound eyes which form so noticeable a feature in its head, there are three other simple little eyes, placed like shining dots at three angles of a triangle below the two feelers.
The mouth, which is a fearful apparatus, consists of nine distinct and well-marked organs; an interior or upper lip, consisting of a plate deeply cleft and capable of opening enormously; two true jaws or powerful mandibles; and two pairs of jointed organs called (maxillary) palpi, and two lower jaws. The mandibles and jaws move laterally from right to left.
The thorax or trunk consists really of three rings. To the first is attached the two front legs; to the second, the two middle legs and the first pair of wings, and to the third, the two hind legs and the second pair of posterior wings. Along the posterior margin is a well marked serrated (spinous) arrangement by means of which the locust adheres and grips forcibly. The trunk appears to be full of a fatty sort of substance.
The abdomen consists of a number of horny segments which are joined together by an elastic membrane, a construction which enables the insect to extend its body several centimetres beyond its normal extent. It can also be increased in thickness.
The front and middle feet of this insect are short and weak, but the length, strength, and formation of the hind legs enable it to take extraordinary leaps. A full-grown locust can jump seven or eight feet in height, whilst it is said to be able to leap more than 200 times the length of its body.
The female is normally larger by ¼ or ½ inch in length than the male, and has a rather thicker body.
The average length of the migratory locust is from 2½ to 3 inches and about ⅜ inch in thickness in the abdomen. Locusts generally lay their eggs in the spring, and the manner in which the females, having selected a favourable site, make an excavation in the earth for depositing their eggs is intensely interesting and wonderful.
At the very extremity of the abdomen the female has two pairs of horny valves or hooks, each pair placed back to back with their points directed outwards, and arranged so that all four hooks can be brought with their points close together. By this means a sharp pointed lever is formed which can be turned around, evolved, and forked. With this apparatus she drills a small hole and by means of a series of muscular efforts and the continuing opening and closing of the valves provided with the formation of the abdomen, she actually bores to a depth of 6 to 7 centimetres, or about 3 inches. Here she deposits her eggs—normally about eighty—regularly arranged in a long cylindrical mass and envelopes them in a spumous or sort of glutinous secretion, so that the whole are quite tapped up and level with the surface of the ground. This substance when dried is more or less impassable and affords protection to the eggs from the elements and secures an easy outlet to the surface for the young locust when hatched. The eggs resemble in shape grains of small rice and are about ¼ inch long.
The eggs hatch in from twenty-five to sixty days, usually about forty days, but the period may vary a little according to temperature, humidity, etc. The young locusts are known as "hoppers," in which stage they pass some forty-five or fifty days before arriving at the fully developed stage known as "fliers." To reach the "flying" or "migratory" stage they pass through six different states, changing the colour of their skin several times, gradually approaching to full growth, and finally growing wings.
They have no quiescent stage, and whilst they are naturally yet incapable of flight, their locomotive powers are very considerable, and they are very destructive, for their voracity is great. Comparatively speaking, the flying locusts do less damage to the growing crops than the hoppers, who devour everything clean before them.
It is interesting to state that the "hoppers" in the first stage are in length about 7 to 9 mm., or not quite one-third of an inch, and that the feelers have thirteen divisions, extending to twenty-seven divisions at full growth.
During the cold weather they usually gather together in thousands, clinging closely to all kinds of vegetation and to each other. In this season the general rule seems to be that comparatively little food is taken of any kind. For the purpose of watching the development of their eggs, several hundred locusts have been opened during the winter months by entomologists, and invariably their cases have been found empty.
Perhaps the most feasible suggestion as to the cause of their migratory impulse is that locusts naturally breed in dry sandy districts in which food is scarce, and are thus impelled to wander in order to procure the necessaries of life.
The rate of travel varies according to circumstances. With an unfavourable wind, or little wind, they seldom travel more than five miles an hour. At other times, when the wind is favourable, they will cover fifteen to twenty miles per hour. When on the wing it is certain that a distance of 1,000 miles may, in particular cases, be taken as a moderate estimate of flight, and whilst, probably, it is often much less, it is sometimes much more. Their height of flight has been variously estimated at from forty to two hundred feet. "A dropping from the clouds" is a common expression used by observers when describing the apparition of a swarm.
It will not be denied that the presence of locusts in force constitutes a terrible plague. They make their appearance in swarms and eat up everything. It is wellnigh impossible to estimate the number in a cloud of locusts, but some idea may be formed from the fact that when they are driven, as sometimes is the case in a storm, into the sea and drowned, so many are washed ashore, that it is said by one observer that their dead bodies formed a bank of nearly 40 miles long and 300 yards wide, and many feet in depth, and the stench from the corruption of their bodies proceeded 150 miles inland.
When a swarm of locusts temporarily settles in a district, all vegetation rapidly disappears, and then hunger urges them on another stage. Such is their voracity that cannibalism amongst them has been asserted as an outcome of the failure of other kinds of food.
Locusts have their natural enemies. Many birds greedily devour them, in fact a migratory swarm is usually followed by myriads of birds, especially sea gulls; they are often found 150 to 200 miles inland. Often a flock of gulls will clean up a "manga" of locusts; they devour them by thousands, and will then go to a neighbouring laguna, take a little water, and throw up all they have eaten, and at a given signal go off again to fill up with more locusts, only to repeat the operation time after time. Predatory insects of other orders also attack them, especially when in the unwinged state. They have still more deadly foes in parasites, some of which attack the fully developed locust, but the greater number adopt the more insidious method of attacking the eggs.
Many inventions have been brought out with the object of exterminating the locusts, some of which, at least, have doubtless been partly successful, but determined and combined effort by the nation and land proprietors is imperative if the remedial and preventive measures proposed are to reap the success hoped for.
The Agricultural Defence Department reports having spent $10,561,540 mn. from 1st January, 1909, to 31st May, 1910, in fighting the locusts. The total area invaded was 135,000,000 hectares (about 337,500,000 acres).
From 1892 to date, and with what is required for the present year, $54,000,000 have been spent in combating locusts and like plagues to agriculture.
