ii4 TRUE TALES OF THE INSECTS. 



excessive abundance in which some of these at times 

 prevail will deny. Tachina- flies especially, will follow 

 the locusts in dense crowds, so thick that not one can 

 rise from the ground without being pursued by several ; 

 and there is no escape from persecution till the victim 

 rises high in the air. 



When food is lacking, whether through excessive 

 multiplication of species, or through the droughts that 

 are not uncommon in the locusts' native habitat, there 

 must needs be the strongest incentive to change of 

 place. Such is the case, under the same circumstances, 

 with other animals normally non-migratory. That 

 hunger will cause locusts to move from place to place 

 in search of food is undoubtedly true, yet it would be 

 a violent presumption to say that a swarm starts on 

 the lengthy journey that they often undertake, in search 

 of food. There seems thus still another factor in the 

 problem, viz. instinctive impulse. It is more than 

 probable there is a certain instinctive prompting to that 

 which is best for the preservation of the species. Fresh 

 breeding-grounds, away from the location of birth, seem 

 desired. The evident disposition often manifested to 

 go in a given direction in spite of contrary winds, or 

 other potent obstacles, is not, to the same extent, sus- 

 ceptible of any other explanation. We have likewise 

 to deal with that most remarkable fact, the return 

 migration of locusts bred in the Temporary region to 



