Migr 



ation 



man and his herds. So great are these swarms that it is 

 difficult to imagine their vastness unless they have been 

 seen. Millions upon millions of these six-legged robbers 

 darken the sky as they move from place to place. In the 

 autumn of 1889 an enormous flight took place over the 

 Red Sea ; it extended for 2000 miles and it was estimated 

 to weigh no less than 42,850 millions of tons. On the 

 following day another and still larger swarm passed in the 

 same direction. In Cyprus alone, during the year 1881, 

 1,600,000,000 locust egg-cases were collected and de- 

 stroyed. Seeing that each case contained several eggs, it 

 is clear that this destruction saved the island from a vast 

 horde of locusts. By the end of the season more than 

 1300 tons of egg-cases had been destroyed, but all this 

 energy on the part of the authorities did not prevent 

 5,076,000,000 egg -cases from being deposited on the 

 island in 1883. 



A natural concomitant of locust swarms is disease, 

 fostered, no doubt, by the decay of millions of the dead 

 bodies of the locusts. These locust migrations take place 

 periodically and at considerable intervals. The instinct 

 to migrate seems to become acute when the swarm has 

 increased to unwieldy proportions and the ranks are 

 thinned considerably by hosts of parasites and also by 

 inclement weather. Should there be a very unfavourable 

 season, the eggs do not hatch from the egg-cases, they 

 simply stay below ground till better times come. 



In locust migration wind is a very important factor and 

 many trial flights are made to test its direction before the 

 main swarm sets out to migrate. As a rule, the insects 

 travel with the wind behind them, and are carried by 

 it without any exertion ; should its direction change, they 

 simply alight, wherever they may be, and await a more 

 favourable opportunity for flight. The immature locusts 

 also migrate, and they do so not by flight but by a series 

 of short hops. The incentive to migration in their case is 

 lack of food and a desire for change. 



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