The locust plague and its suppression / by Æneas Munro.

  • Munro, Aeneas.
Date:
[1899]
Catalogue details

Licence: Public Domain Mark

Credit: The locust plague and its suppression / by Æneas Munro. Source: Wellcome Collection.

    58/388 page 34
    night has a great attraction for them. No doubt, with clear bright moonlight they do ascend and practise nocturnal flights,—these are, however, exceptional,—but under what circumstances or for what special objects we do not know. This peculiarity more especially will be found towards the latter part of their sojourn, and probably is therefore connected with their “returning” journey, which is subject to the same uncertainty as to date, rather than at the beginning, when, as a rule, they rest at night. 78. Flight invisible to the naked eye.—In regard to the height at which locusts fly there is possibly something yet to be learnt. As a rule, people only notice them when they are within easy seeing distance ; but it not unfrequently happens that, for example, on clear days they may, by the aid of an opera-glass or telescope, be observed in myriads high up where the unaided eye cannot detect them. Thus there passed over Johannesburg on the 15th November 1896, and twice in October 1898, a large swarm in evidently a high stratum of the atmosphere, and of which there was no evidence in the town by the unaided eye of their passage. A large company (the first of the season en masse) did pass through Johannesburg about ten days before that above stated, and then it was observed that their colour was more reddish than usual. There may thus be said to be three kinds of swarms : (a) Invading company, (b) Local company, and (c) Returning company. 79. Rate of flight .—The speed at which they move in flight varies also. No doubt the wind exercises a considerable influence, but they can fly pretty quick, even when the wind is apparently or per- ceptibly not moving rapidly. They can be often seen going at the rate of twelve miles an hour, and at other times they seem to enjoy hovering about. 80. Flight affected by atmospheric influences.—In making any estimate of value as regards either the height at which they fly or the speed they make, it is requisite to take into account the size of the flight and the rate of speed of the wind and currents in the strata of the atmosphere. Thus a company on the wing with an unbroken front of fifty miles by perhaps a hundred in length, may take three days to pass, similar smaller swarms had come up irom the sterile plains f of the south ; and many trees had been entirely stripped of their leaves. Of course this swarm cannot be compared to those of the Eastern world, yet it was sufficient to make the well-known description of their ravages more intelligible. I have omitted, perhaps, the most striking part of the scene—the vain attempt of the poor cottagers to turn the stream aside. Many lighted fires, and with the smoke, with shouts and waving of branches, they endeavoured to avert the attack.’ 1 Swarms of locusts sometimes overrun the more central plains of this continent. In these cases, and likewise, as it appears, in all parts of the world, the locusts are bred in desert plains, and thence migrate towards a more fertile country.
    No text description is available for this image
    No text description is available for this image
    No text description is available for this image