ANTS. 71 
for their especial benefit. When the beetle is descried on 
its way through the air to eat up the heart of the flower, the 
guard turns out, presents arms (and legs), and squirts a little 
of that nasty formic acid in the face of the invading foe, 
with the effect of causing Mr Beetle to regret that he ever 
came that way. In a day or two the tender florets have 
passed the critical stage, protection from that kind of attack 
is no longer required, the tiny fountains of nectar have dried 
up—being no longer required—and the ants make their way 
to a similar feast elsewhere. 
In some few other cases—the last there is time for 
referring to in this Address—one species of ant has been 
pitted by the plant against another. Some of the leaf- 
cutting ants make it a practice to ascend a certain tree, and not 
to leave the tree until they have stripped off every leaf it bore. 
This is not at all a good thing for the tree, which cannot 
get on at all well without its leaves. So it has encouraged 
the visits of another kind of ant, also of warlike propensities 
like the one just now referred to. It provides these warriors 
with a small but reliable supply of nectar, and it also seems 
to make special provision for housing them rent free, so to 
speak, The tree grows big thorns, which were probably 
intended, in the first instance, to make the tender shoots 
unpleasant eating to some herbivorous animals—probably 
during some arid climatal conditions. Nowadays the ants 
take up their abode in the hollow centre of these thorns. 
Mr W. C. Crawford suggests to me that the excretion of 
formic acid from the ants may have had something to do 
with developing these thorns, and in thereby indirectly 
helping them to grow to an abnormal size, just as any other 
irritant in the growing tissues of a plant is very apt to do. 
Anyway, the ants take up their abode in these thorns, 
forming a standing army there; and when the leaf-cutters 
begin to ascend the tree on one of their marauding expedi- 
- tions, the guards come forth to battle, and the invading force 
is usually repelled with great slaughter (see Belt, Z'he 
Naturalist in Nicaragua, p. 218). 
I wish there had been more time to deal with this subject 
in the present Address, and more space available for printing 
