126 THE INSECT WOELD. 



of 590,490,000, will yield a progeny of 53,142,100,000 ; at the 

 seventh, we shall thus have 4,782,789,000,000 ; and the eighth 

 will give 441,461,010,000,000. This immense number increases 

 immeasurably when there are eleven generations in the space of a 

 year. Fortunately a great many carnivorous insects wage fierce 

 war against the plant-lice, and destroy immense numbers of them. 

 Thus they are kept in check, and prevented from multiplying 

 inordinately. To show with what prodigious abundance the re- 

 production of these little but formidable parasites must go on, we 

 will relate a fact which was made known to us by M. Morren, 

 Professor in the University of Liege. 



The winter of 1833 34 had been extremely warm and dry ; 

 whole months had passed without any rain. A well-known savant, 

 Van Mons, had foretold, as early as the 12th of May, that all the 

 vegetables would be devoured by plant-lice. On the 28th of 

 September, 1834, at the moment when the cholera had began to 

 spread its ravages over Belgium, all of a sudden a swarm of plant- 

 lice showed themselves between Bruges and Ghent. They were 

 to be seen the next day at Ghent, hovering about in troops, in 

 such quantities that the daylight was obscured. Standing on the 

 ramparts, one could no longer distinguish the walls of the houses 

 in the town, so covered were they with plant- lice. The whole 

 road from Antwerp to Ghent was rendered black by innumerable 

 legions of them. They appeared everywhere quite suddenly. 

 People were obliged to protect their eyes with spectacles and their 

 faces with handkerchiefs, to keep off the painful and disagreeable 

 tickling caused by them. The progress of these insects was inter- 

 rupted by mountains, hills, even by undulations of land of very 

 slight elevation, but sufficient to have an influence on the wind. M. 

 Morren thinks that they came from a great distance, and that they 

 arrived in Belgium by the sea-coast. Whatever be the explana- 

 tion of the phenomenon, it establishes sufficiently the prodigious 

 multiplication of these little insects. 



There is another trait, and without doubt the most curious in 

 the history of the aphides, to which we have still to call the atten- 

 tion of the reader : we mean the relations which exist between 

 them and the ants. 



No one can have failed to observe ants frequenting those places 



