272 INSECT MISCELLANIES, 



winter, to escape to a more genial climate ; thouo-li 

 the migration has the effect, like that of the locusts, 

 of reducing an overgrown population, and at the 

 same time of supplying food to many animals who 

 might otherwise have starved. In their journeys, 

 they always endeavour to keep in a direct line ; and 

 hence multitudes of them perish in their endeavours 

 to cross lakes and rivers. If they are disturbed or pur- 

 sued while swimming over a lake, and their phalanx 

 chances to be separated by oars or poles, they will 

 not recede; but keep swimming directly on, and soon 

 get into regular order again. So obstinate, indeed, 

 are they in holding on their direct course, that they 

 have sometimes been known to try to pass over a 

 vessel. This army of rats moves chiefly by night, 

 or early in the morning; and makes such destruction 

 among the herbage, that the surface of the ground 

 over which they have passed appears as if it had 

 been burned. Their numbers have at times induced 

 the people of Norway to believe that they descended 

 from the clouds ; and the multitudes that are some- 

 times found dead on the banks of rivers, or other 

 places, corrupt the whole atmosphere around *. 



We recollect another remarkable migration of a 

 different species of animal also towards the sea- 

 coast, but for a very different purpose, and we men- 

 tion it here more particularly, because it will lead 

 us back by a natural transition to families of insects 

 influenced by similar motives, — we refer to the land- 

 crab of the West Indies {Ocipoda rwicola, La- 

 treille). The usual residence of this species is the 

 inland mountains and woods, where they live in 

 holes dug by themselves. Annually, about the 

 months of April and May, they set forth in a body, 

 often consisting of some millions, for the sea-coast. 

 They always march in a direct line to their place of 

 * Pennant, Arctic Zoology, 



