Ch. V.] NESTS OF THE LEAF-CUTTERS. 75 



citron (Citrus medicus), on the other hand, are only found 

 where they have been planted and protected by man ; 

 and, were he to give up their cultivation, the only 

 species that would ultimately withstand the attacks of 

 the ants, and obtain a permanent footing in Central 

 America, would be the lime. The reason why the lime 

 is not so subject to the attacks of the ants is unknown ; 

 and the fact that it is so is another instance of how little 

 we know why one species of a particular genus should 

 prevail over another nearly similar form. A little more 

 or less acridity, or a slight chemical difference in the 

 composition of the tissues of a leaf, so small that it is 

 inappreciable to our senses, may be sufficient to ensure 

 the preservation or the destruction of a species through- 

 out an entire continent. 



The ravages of this ant are so great that it may not 

 be without interest for me to enter upon some details 

 respecting the means I took to protect my own garden 

 against their attacks, especially as the continual warfare 

 I waged against them for more than four years made 

 me acquainted with much of their wonderful economy. 



In June, 1859, very soon after the formation of my 

 garden, the leaf-cutting ants came down upon it, and at 

 once commenced denuding the young bananas, orange and 

 mango trees of their leaves. I followed up the paths of 

 the invading hosts to their nest, which was about one 

 hundred yards distant, close to the edge of the forest. 

 The nest was not a very large one, the low mound of 

 earth covering it being about four yards in diameter. 

 At first I tried to stop the holes up, but fresh ones were 

 immediately opened out : I then dug down below the 

 mound, and laid bare the chambers beneath, filled with 



