Animals As Soil Builders

Animal life contributes much more to the building of soils than seems possible at first thought. Eventually every animal and insect returns to the soil, from which it came. The addition of animal matter to the soil is not nearly so evident as the addition of vegetable matter from decaying plants ; yet, when we reflect upon it, the excrements and the remains of all creatures upon the earth must aggregate a considerable amount. Of no small importance also, are the burrows, channels, holes, etc., in which animals live or by which they feed. Ants, moles, gophers, woodchucks, and the like are insignificant soil builders as individuals, but in the aggregate they have great influence. Ants are abundant on many of the lighter soils and often exercise a profound influence on their structure and agricultural value. Shaler has calculated that ants bring to the surface of a four-acre field, in Cambridge, Massachusetts, enough sand and fine soil to cover the entire area one-fifth inch deep each year. This is probably a larger amount of material than ants move in most places, although those of us who have had to fight ants in lawns are quite willing to accept these figures; but they call our attention to the insidious and far-reaching influence that these tiny creatures may exert.

Since the material brought to the surface by the smaller ants is mostly fine sand and smaller particles of soil, they being unable to move the larger particles, it is evident that the texture of the surface soil must be greatly modified by their industry. The mounds built by the large black and brown hill-building ants are often two feet in height and four feet in diameter. They are composed mostly of soil brought from below, mixed with bits of leaves and bark. They are being washed down constantly by rains and added to the surface soil. These ants usually build a new mound each year. Furthermore, the subterranean burrows and channels of ants, penetrating as they do from several inches to many feet, have a pronounced effect upon the texture of the soil, and upon its aeration. The burying beetle, crayfish, woodchuck, chipmunk, mole, gopher, prairie dog, ground squirrel, badger, and other burrowing animals and insects, all contribute largely, in the aggregate, to the movement and aeration of soils, the latter four being especially abundant west of the Mississippi.

Gophers have honeycombed millions of acres, and prairie dogs and ground squirrels have been no less industrious. However injurious these animals may be otherwise, and however difficult may be the task of exterminating them so that crops can be grown, they certainly serve a useful purpose in mixing the subsoil with the surface soil and promoting better drainage and aeration. Thousands of acres of land in the United States have been submerged by the erection of beaver dams and their value for agricultural purposes has been profoundly influenced thereby. The beaver is no longer an important factor in soil building with us, but he has contributed very largely in the past. The Important Service of Angleworms. — The most important soil builder among animals is the angleworm or earthworm. Of these there are many kinds, from the big, snaky "night walker," that the fisherman with a torch finds crawling along the ground at night, to the tiny red ones beneath the pile of old manure. In South Africa some earthworms are two feet long. All of them are most industrious soil workers.

After a rainy night, especially in early spring, the ground may be thickly strewn with their castings. On digging down in most moist soils a labyrinth of angleworm channels will be found. These burrows go more than five or six feet below the surface. Angleworms benefit farm soils in several ways. The channels that they make loosen, aerate and drain the soil to a considerable depth, far deeper than the subsoil plow works. The small roots and rootlets that reach deep into the subsoil usually follow the worm burrows, This is particularly true of tenacious soils, in which angleworms most frequently work. They are rarely numerous in very light, sandy soils because these do not contain a sufficient quantity of vegetable matter upon which they may feed. Again, the soil is fined by being passed through the worms.

In making these channels the worm swallows the soil for the purpose of using as food the decaying vegetable matter it contains. As it passes out through the worm this soil is ground, as grain is ground in a chicken's gizzard. Charles Darwin estimated that the angleworms in English soils passed through their bodies and ground over ten tons of soil per acre each year ; that is, they deposited about one-fifth of an inch of castings over the entire surface each year. This is the richest kind of top-dressing. He estimated that there are about 50,000 earth worms in each acre of English garden land, and about 25,000 in each acre of meadow land. Our American soils are as full of " bait worms" as the English soils, and their influence on our agriculture must be fully as pronounced as that assigned to them by the great scientist.