INTRODUCTORY. 5 
personal strength for labours for which that strength 
is wholly inadequate, he again sees and bears in 
mind both the cause and its effect. When, once more, 
the termite gains access to our dwellings, and honey- 
combs the woodwork so completely that not one 
cubic inch of solid material is left untouched, we 
cannot fail to take note of the insect which has 
caused so great an amount of damage, both the 
worker and its work, in fact, being not merely notice- 
able, but forced upon our notice. 
But it is far otherwise in the case of our natural 
friends, whose work, for the most part, although 
equally influential and important, is carried on in 
secret. Ifa flock of birds detect the first small body 
of locusts, possible progenitors of a future legion, and 
destroy them before they can find an opportunity of 
laying their eggs, man is none the wiser. Those 
birds, by that one act, have saved him, perhaps, from 
the loss of a whole year’s produce; but he knows not 
the danger which he has escaped. Ifa parasite prey 
upon the parasite, and diminish its capabilities for mis- 
chief by reducing its numbers, man is unacquainted 
with the inestimable service thus rendered to him. 
He finds, later on, that the swarms of locust or tsetse 
do not make their dreaded appearance, but he re- 
mains in ignorance of the cause which has saved him 
from their ravages. He sees, perhaps, the insect- 
ivorous bird, and he sees the hyper-parasite, but he 
does not connect them with the immunity which he 
enjoys from the depredations of the creatures so 
injurious to his interests. And thus, constantly 
