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.