CHAPTER XVI. 



ON THE EXCESSIVE APPEARANCE OF PARTICULAR INSECTS. 



Natural balance in the relative numbers of living creatures (357). 

 This balance occasionally disturbed (388). Excessive appear- 

 ance of Aphis vastator (389). Instance at Brighton (390). 

 Insect plagues recorded in the Old Testament (391). Kirby and 

 Spence (392). Ravages of the May-beetle (393, 394). Ravages 

 of several species of insects (395, 396). Bostrichus typographus 

 (397). Locust plagues (398, 399). Wasps (401). Honeydew 

 (402). Controlling agents (404). The exaggerated increase of 

 particular insects not continuous (405). 



(387.) WE have now found that the gangrene of the 

 potatoe is to be attributed to an excessive increase of the 

 Aphis vaslator. As a general rule, Nature has exquisitely 

 contrived that every organic body should bear certain 

 relations to other organic bodies, and hence the earth 

 remains tenanted with a great variety of beings, and none 

 are in excess to the detriment of the rest. 



(388.) In particular instances, however, this balance 

 of tenantry is disturbed, and occasionally some one insect 

 becomes too redundant, and occupies more than its allotted 

 space. 



(389.) The excessive appearance of the Aphis vastator 

 is an instance of this character ; for to such an extent has 

 it been recently found, that in a field of beet, less than a 

 quarter of an acre in extent, there were countless millions 

 of this parasite. It appears that some time previous to a 

 thunder-storm this Aphis is apt to fly ; and on September 



