138 
Psyche 
[December 
If the trees and ants are interconnected possibly one or the 
other of the two basal factors of animal success may be involved; 
the gaining of food for energy of the individual ant or else the 
proper conditions for reproduction and the continuance of the 
species. One mound may not obtain food enough to keep up the 
depletion in population, while another mound may obtain a sur- 
plus of food and be able not only to maintain itself but actively to 
colonize the surrounding neighborhood with new and rapidly 
growing mounds. 
Unfortunately little is known about the food of this par- 
ticular mound building ant. In this region it is observed that 
the ants climb the trees near their mounds and go out on the 
branches and leaves; it is observed that they get honey dew 
from some kinds of aphids or plant lice and from the black leaf 
hopper Vanduzea arcuata Say. They are seen to drag various 
dead insects into their mounds. 
It may be assumed that these ants depend greatly upon 
trees for their food supply which is partly at least carbohydrate 
in nature. In artificial formicaries many kinds of ants can be 
kept very long periods when fed chiefly sugar and water or honey. 
If it be granted that ants derive their energies from food 
supplied by trees, there may be an inverse ratio between the 
food got and the work done in getting it, according to the height 
and food-supplying character of the trees. If small young trees 
give as much food per unit of leaf or photosynthetic element as 
do the old trees, then the labor of going up the old tree to get the 
food will be greater than going the short distance up the young 
tree; and on an exceedingly tall tree, the ants might use up all 
the energy acquired before they ever got down to the ground 
again. Also, it may well be that the tender young shoots of 
young trees feed more aphids and yield more sap than is available 
from like area of the twigs of an old tree, so that it would ad- 
vantage the ant to visit the young rather than the old tree. 
From the data given in “Bau und Leben unserer Wald- 
baume,” M. Buesgen, Jena, 1917, we infer that the total photo- 
synthetic area of a young tree five or six years old may be some 4 
square meters; but of an older tree 13 to 14 meters in height, from 
8 to 24 square meters according as to whether it grows under 
