220 THE NATURALIST IN NICARAGUA. [Ch. XII, 



tinually employed going from one to another, examining 

 them. When an ant finds one sufficiently advanced, it 

 bites the small point of attachment ; then, bending down 

 the fruit-like body, it breaks it off and bears it away in 

 triumph to the nest. All the fruit-like bodies do not 

 ripen at once, but successively, so that the ants are kept 

 about the young leaf for some time after it unfolds. 

 Thus the young leaf is always guarded by the ants ; and 

 no caterpillar or larger animal could attempt to injure 

 them without being attacked by the little warriors. The 

 fruit-like bodies are about one-twelfth of an inch long, 

 and are about one-third of the size of the ants ; so that the 

 ant bearing one away is as heavily laden as a man bear- 

 ing a large bunch of plantains. I think these facts show 

 that the ants are really kept by the acacia as a standing 

 army, to protect its leaves from the attacks of herbivorous 

 mammals and insects. 



The bull's-horn thorn does not grow at the mines in 

 the forest, nor are the small ants attending on them 

 found there. They seem specially adapted for the tree, 

 and I have seen them nowhere else. Besides the Pseudo- 

 myrma, I found another ant that lives on these acacias ; 

 it is a small black species of Or ematog aster, whose habits 

 appear to be rather different from those of Pseudo- 

 myrma. It makes the holes of entrance to the thorns 

 near the centre of one of each pair, and not near the end, 

 like the Pseudomyrma ; and it is not so active as that 

 species. It is also rather scarce ; but when it does occur, 

 it occupies the whole tree, to the exclusion of the other. 

 The glands on the acacia are also frequented by a small 

 species of wasp (Polylia occidentals). I sowed the seeds 

 of the acacia in my garden, and reared some young 



