The Earth as Modified by Human Action eBook

It should be added that the writer quoted, and all others who have discussed the subject, have, so far as I know, overlooked one very important element in the fertilization produced by earthworms.  I refer to the enrichment of the soil by their excreta during life, and by the decomposition of their remains when they die.  Themanure thus furnished is as valuable as the like amount of similar animal products derived from higher organisms, and when we consider the prodigious numbers of these worms found on a single square yard of some soils, we may easily see that they furnish no insignificant contribution to the nutritive material required for the growth of plants. [Footnote:  I believe there is no foundation for the supposition that earthworms attack the tuber of the potato.  Some of them, especially one or two species employed by anglers as bait, if natives of the woods, are at least rare in shaded grounds, but multiply very rapidly after the soil is brought under cultivation.  Forty or fifty years ago they were so scarce in the newer parts of New England, that the rustic fishermen of every village kept secret the few places where they were to be found in their neighborhood, as a professional mystery, but at present one can hardly turn over a shovelfull of rich moist soil anywhere, without unearthing several of them.  A very intelligent lady, born in the woods of Northern New England, told me that, in her childhood, these worms were almost unknown in that region, though anxiously sought for by the anglers, but that they increased as the country was cleared, and at last became so numerous in some places, that the water of springs, and even of shallow wells, which had formerly been excellent, was rendered undrinkable by the quantity of dead worms that fell into them.  The increase of the robin and other small birds which follow the settler when he has prepared a suitable home for them, at last checked the excessive multiplication of the worms, and abated the nuisance.]

The carnivorous and often herbivorous insects render another important service to man by consuming dead and decaying animal and vegetable matter, the decomposition of which would otherwise fill the air with effluvia noxious to health.  Some of them, the grave-digger beetle, for instance, bury the small animals in which they lay their eggs, and thereby prevent the escape of the gases disengaged by putrefaction.  The prodigious rapidity of development in insect life, the great numbers of the individuals in many species, and the voracity of most of them while in the larva state, justify the appellation of nature’s scavengers which has been bestowed upon them, and there is very little doubt that, in warm countries, they consume a larger quantity of putrescent organic matter than the quadrupeds and birds which feed upon such aliment.

INJURY TO THE FOREST BY INSECTS.

The action of the insect on vegetation, as we have thus far described it, is principally exerted on smaller and less conspicuous plants, and it is therefore matter rather of agricultural than of geographical interest.  But in the economy of the forest European writers ascribe to insect life an importance which it has not reached in America, where the spontaneous woods are protected by safeguards of nature’s own devising.