PLANT-EATING INSECTS 207 



The workers also establish communication between the 

 internodal chambers by boring through the septa or 

 partitions. They seldom or never leave the tree, which 

 itself supplies them with food in the form of little egg- 

 shaped bodies which are produced just below the bases of 

 the leaf-stalks. The ants detach these as they ripen, and 

 either eat them immediately, or store them in the hollow 

 chambers of the stem for future use. When these egg- 

 shaped bodies are present in numbers on a tree, it is a 

 sure sign that the ants, which belong to the genus Azteca, 

 are not in residence. 



Not the least remarkable fact connected with these 

 ants of the Acacia and Cecropia is that they actually 

 protect their trees from the ravages of leaf- cutting ants 

 and other marauders. Despite their diminutive size, the 

 tree-dwellers are very fierce and pugnacious, and will not 

 tolerate trespass upon their domains. " So soon as this 

 standing army of ants detects the foe" (writes the great 

 botanist Anton Kerner von Marilaun) "it commences 

 offensive operations, like the garrison of a fortress, and by 

 biting and squirting formic acid frightens the invader 

 away." These interrelations of ants and plants have 

 doubtless been gradually perfected, in the course of ages, 

 through the agency of natural selection. In tropical 

 America, leaf-cutting ants are a terrible scourge, and can 

 strip a tree of its foliage in the space of a few hours. 

 Clearly, therefore, a tree which possessed a large and 

 easily satisfied ant-garrison, bent upon keeping intruders 

 at bay, would be more likely to survive than another of 

 the same species to which no such ants resorted. Thus, 

 any variation on the part of a tree calculated to attract 

 ants of the right sort would tend to be established 

 and perfected. These marvellous interrelations probably 

 arose in some such manner ; but to say that the ants 



