MUTUAL AID AND COMMUNAL LIFE AMONG ANIMALS 379 



ing account of the symbiosis of the Aztec ants and the imbauba 

 tree: 



"In the forests of South America grow the imbauba or so-called 

 candelabra trees, species of the genus Cecropia, which well deserve 

 their name, 'candelabra,' from the curious appearance given them 

 by the outspringing bare branches, each bearing a tuft of leaves at the 

 free end. These leaves are often attacked by the leaf-cutting ants of 

 the genus (Ecodoma, which roam by 

 tens of thousands over the various 

 plants of the forest biting off the 

 leaves, that they may fall to the ground, 

 where they are again seized, bitten into 

 pieces and the pieces carried into the 

 nests of the ants. In the nests they 

 serve as a medium on which grow cer- 

 tain molds or fungi, much liked by the 

 ants. The candelabra tree protects it- 

 self from these leaf-robbing enemies by 

 an association with another ant species, 

 Azteca instabilis, which finds safe dwel- 

 ling places in the hollow trunk of the 

 tree and a special supply of food in a 

 brownish fluid secreted by it. Along 

 the tree trunk occur in regular order 

 little pits through which the female 

 Azteca can easily bore into the interior, 

 where she lays her eggs and establishes 

 colonies, so that soon the interior of 

 the whole trunk swarms with ants 



which rush out whenever the tree is shaken. But this alone would not 

 serve to protect the imbauba from the leaf cutters, for how could the 

 Aztecs dwelling inside the tree know of the presence of the light-footed 

 leaf-cutters without? But this is arranged for by the development on 

 the outside of the tree, at the very points where the danger is greatest, 

 namely, on the petioles of the younger leaves, of peculiar little hairy 

 growths from which project small white grains which are very nutri- 

 tious and not only eagerly eaten by ants, but garnered by them to carry 

 into their nests, presumably as food for their larva?. Thus right where 

 protection is most needed the plant has developed a special organ 

 attractive to the fierce Aztec ants, so that their constant presence at 



FIG. 233. Piece of a branch of 

 the Imbauba tree, Cecropia, the 

 leaves cut away, showing at 

 the base of each petiole the 

 small tuft on the food ; at the 

 right some of this ant food en- 

 larged. (After Schimper.) 



