MIGRATION AND DISPKRSAL OF INSECTS : ORTHOPTERA. 17 



ci'OSSGd the Vaal river in 1871, sliortly after the discovery of the 

 diamond fields. The country was devastated by youn,;? locusts, and a 

 swarm made its appearance on the banks of the Vaal River. For 

 several days the locusts travelled up the stream, reaching an abrupt 

 bend in the river, where a number of rocks cropped out. At this 

 point they stopped some time, but at last went on again. Three days 

 afterwards, however, they returned to the same bend of the river, 

 plunged in vast multitudes into the stream, and, assisted by a strong 

 current and by the waterplants growing there, they managed to effect 

 a crossing, although many were drowned and carried away by tho 

 flooded river. 



The same lady states that these " Voctgangcrs " have been known 

 to cross the Orange river where it was several yards in breadth. 

 Attaching themselves to one another in vast numbers, they formed 

 large floating islands, and it is possible that some of these reached the 

 opposite bank in safety. Sharp says that "it is a common practice 

 for young locusts to form a bridge over a moderately broad stream by 

 plunging indiscriminately into it and, holding on to each other, grap- 

 pling like drowning men at sticks or straws, or, in fact, anything that 

 comes within reach and that will assist in floating them. Meanwhile, 

 those from behind are eagerly pushing forward over the bodies of those 

 that are already in the stream, and hurry on to the front, until at 

 length, by this process, they reach the opposite bank of the river. 

 Thus, a floating mass of living locusts is stretched across the stream, 

 forming a bridge over which the whole swarm passes. In this manner 

 few, comparatively speaking, are drowned, l^ecausc the same in- 

 dividuals do not remain in the water during the whole of the time 

 occupied by the swarm in crossing, the insects continually changing 

 places with each other, those that are beneath endeavouring to reach 

 the surface by climbing over others, whilst those above them are, in 

 their turn, being forced below." Donzingk relates having seen 

 young locusts swim over the Dnjestr for a distance of 1|- German 

 miles, in layers 7 or 8in. in thickness. 



There seems to be considerable doubt as to the rate at which 

 larval locusts travel. Finot is logical in assuming that this varies 

 greatly with age, and depends to a great extent also on food and 

 temperature conditions. Following Durand, he asserts it as about 

 1 kilometre per day after the larva has reached the age of 15 days. 

 Hydon and Donzingk give about '975 of an English mile per hour, a 

 distance possibly very much too great even for the most active. 

 Techemewsky asserts that they only advance about 350ft. per day on 

 grass land. 



It is, however, in the winged state that the greatest number of 

 " locust " migrations takes place. Biblical history has made us con- 

 versant with the vast size of the migratory hordes which frequently 

 occur in Asia and Africa. The adult winged locust is able to travel 

 very great distances, and there seems to be very clear evidence that 

 the migratory swarms often travel by night. It is possible, however, 

 that they cannot cover the whole of the distance from the country 

 they leave to that to which they are bound without stoppages by the 

 way, and the attempt to take too long journeys must often end 

 disastrously, for they have frequently been found in the sea in 

 immense numbers at a considerable distance from land, having 



