INSECT COMMUNITIES 277 



have been in abeyance, perhaps for a decade, resume their 

 sway, and the swarms set forth along the same courses 

 which were followed by their ancestors. Locusts seem to 

 rely mainly upon air currents in their journeyings, and to 

 make little use of their wings. They are known to make 

 trial flights in order to ascertain the direction of the wind. 

 When this proves favourable, the whole swarm rises, and 

 is carried forward without effort. The migratory instinct 

 in some locusts arises in the young before the wings are 

 developed, and long journeys are accomplished afoot. Dr. 

 David Sharp, quoting from an account by Mrs. Barber, 

 gives interesting particulars as to the manner in which 

 rivers are crossed by these youthful emigrants, which are 

 called " Voetgangers " by the Dutch in South Africa. 

 " It is a common practice for the young locusts to form 

 a bridge over a moderately broad stream by plunging 

 indiscriminately into it and holding on to each other, 

 grappling like drowning men at sticks or straws, or, in 

 fact, anything that comes within their 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 hurrying 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, com- 

 paratively speaking, are drowned, because the same 

 individuals 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 are endeavouring to reach the surface by 

 climbing over others, whilst those above them are, in their 

 turn, being forced below. Locusts are exceedingly tena- 

 cious of life, remaining under water for a considerable time 



