140 MINUTE ORGANISMS. 
United States, dead trees, especially of the spike-leaved kinds, 
too much decayed to serve for timber, and which, in that state, 
are worth little for fuel, are often allowed to stand until they 
fall of themselves. Such stubs, as they are popularly called, are 
filled with borers, and often deeply cut by the woodpeckers, 
whose strong bills enable them to penetrate to the very heart of 
the tree and drag out the lurking larvee. After a few years, 
the stubs fall, or, as wood becomes valuable, are cut and carried 
off for firewood, and, at the same time, the farmer selects for 
felling, in the forest he has reserved as a permanent source of 
supply of fuel and timber, the decaying trees which, like the 
dead stems in the fields, serve as a home for both the worm and 
his pursuer. We thus gradually extirpate this tribe of insects, 
and, with them, the species of birds which subsist principally 
upon them. Thus the fine, large, red-headed woodpecker, 
Picus erythrocephalus, formerly very common in New England, 
has almost entirely disappeared from those States, since the 
dead trees are gone, and the apples, his favorite vegetable food, 
are less abundant. 
There are even large quadrupeds which feed almost exclu- 
sively upon insects. The ant-bear is strong enough to pull 
down the clay houses built by the species of termites that con- 
stitute his ordinary diet, and the curious ai-ai, a climbing quad- 
ruped of Madagascar, is provided with a very slender, hook- 
nailed finger, long enough to reach far into a hole in the trunk 
of a tree, and extract the worm which bored it.* 
Minute Organisms. 
Besides the larger inhabitants of the land and of the sea, the 
quadrupeds, the reptiles, the birds, the amphibia, the crustacea, 
the fish, the insects, and the worms, there are other countless 
forms of vital being. Earth, water, the ducts and fluids of 
vegetable and of animal life, the very air we breathe, are peo- 
pled by minute organisms which perform most important fune- 
* On the destruction of insects by reptiles, see page 125 ate. 
