Forest Preserve District of Cook County, Illinois
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Life in the Soil
Nature Bulletin No. 84   September 21, 1946
Forest Preserve District of Cook County
Clayton F. Smith, President
Roberts Mann, Superintendent of Conservation

If we examine a crumb of fertile soil beneath a microscope we find that, like a drop of water from a pond, it is literally alive with bacteria, protozoa, round worms and other minute living things. These, with the fungi and tiny mites, are all-important as reducers of the plant and animal remains, on and in the soil, to tiny particles of food for other plants and animals. This is commonly called "rotting."

Also important are the higher forms of insects which hibernate or dwell in the soil. The ants are most important but cicadas, grasshoppers, crickets, caterpillars, beetles and wasps are other insects that serve as channellers or as mixers, or both -- burrowing thru the soil and feeding on other insects or on plant roots. One square foot of soil examined was found to contain almost 200 species of insects and primitive animals, in quantities which would indicate an average of more than 20 million individuals per acre.

Many higher animals, including woodchucks, skunks, gophers, moles, shrews and mice, play important roles as burrowers, but numerous and most valuable are the lowly earthworms. Eating their way thru, to depths as much as 6 or 8 ft. in winter, they bring mineral subsoil to the top during the warmer months and drag plant particles, such as grass and dead leaves, down below. They enrich and mix the soil while increasing its porosity so that water and air can enter.

It has been found that mixed stands of trees with heavy undergrowth produce better timber yields than "pure" stands of one species cultivated like cabbages. Some trees of little value for lumber are the most beneficial to highly desirable soil insects and animals. Minor trees, shrubs, herbaceous plants, mosses, lichens and algae conserve moisture and contribute debris valuable as food for the soil and its fauna. The plant rootlets are eaten or die to leave a network of water channels.

Unburned, ungrazed and uncultivated, an acre of soil supports a great quantity and variety of plants, a vast complex society of insects, and a smaller number of animals. Several acres can support only a few predators -- including man himself. All are inter-related and interdependent. All return their excreta and their dead bodies to the soil. Are you ready?

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