PLANTS THAT KEEP AN ARMY 55 
extra protection to the acacia. Of course, their 
milk cows, which are species of beetles, also a kind 
of caterpillar, and cochineal, must be stationed 
out in herds on various parts of the tree; and each 
herd is separated and carefully guarded by a herds- 
man; and he, in turn, is accompanied by several 
small animals, obviously as watch-dogs. As a 
colony of ants and their helpers are capable of 
destroying hundreds of caterpillars and grasshop- 
pers a day, and as they work day and night, the 
tree is well protected. 
In still another way do the servants of the plant 
prove a benefit to it: in addition to destroying or 
driving away the larger marauders they eat the 
minute parasites. 
There are plants which do not produce honey 
with which to pay their armies; in such a case it is 
usually found that the plant is already inhabited 
by a number of insects, which can supply milk and 
meat to the warrior inhabitants; and so slave-hold- 
ing ants take possession of the tree as a desirable 
dwelling-place on which to raise their army of 
allies. One form of beetle, raised in the under- 
ground nests of these ants, secretes and produces 
a sweet fluid, that might be an intoxicant. 
Another plant of the tropical regions which 
keeps not only its own standing army, but also its 
