292 ORTHQPTERA chap. 



locally to a great extent — very often for one or two seasons only, 

 — and are then called locusts. The true migratory locusts are 

 species that have gregarious habits strongly developed, and 

 that move over considerable distances in swarms. Of these there 

 are but few species, although we hear of their swarms in many 

 parts of the world. 



The migratory locusts do much more damage than the endemic 

 species. In countries that are liable to their visitations they 

 have a great influence on the prosperity of the inhabitants, for 

 they appear suddenly on a spot in huge swarms, which, in the 

 space of a few hours, clear off all the vegetable food that can be 

 eaten, leaving no green thing for beast or man. It is difficult 

 for those who have not witnessed a serious invasion to realise the 

 magnitude of the event. Large swarms consist of an almost 

 incalculable number of individuals. A writer in Nature -^ states 

 that a flight of locusts that passed over the Eed Sea in jSTovember 

 1889 was 2000 square miles in extent, and he estimated its 

 weight at 42,850 millions of tons, each locust weighing -^^ of an 

 ounce. A second similar, perhaps even larger, flight was seen 

 passing in the same direction the next day. That such an 

 estimate may be no exaggeration is rendered probable by other 

 testimony. From official accounts of locusts in Cyprus we find that 

 in 1881,- up to the end of October, a, 600,000,000 egg-cases had 

 been that season collected and destroyed, each case containing a 

 considerable number of eggs. By the end of the season the weight 

 of the eggs collected and made away with amounted to over 1300 

 tons, and, notwithstanding this, no less than 5,076,000,000 egg- 

 cases were, it is believed, deposited in the island in 1883. 



When we realise the enormous number of individuals of which 

 a large swarm of locusts may consist we can see that famine is 

 only a too probable sequence, and that pestilence may follow — as 

 it often has done — from the decomposition of the bodies of the 

 dead Insects. This latter result is said to have occurred on some 

 occasions from locusts flying in a mass into the sea, and their 

 dead bodies being afterwards washed ashore. 



Locust swarms do not visit the districts that are subject to 

 their invasions every year, but, as a rule, only after intervals of 

 a considerable number of years. It has been satisfactorily 



^ Carrutliers in Nature, xli. 1889, p. 153. 

 2 Blue-hook, C, 4960, 1887 ; and P. ent. Soc. London, 1881, p. xxxviii. 



