The larger soil organisms are responsible for considerable mechanical mixing and weathering of soil. The wedge-like action of roots and other underground plant organs, widens the fissures in rocks and the compacted soil so that they are more susceptible to other forms of weathering. Rodents, insects and worms turnover great amounts of soil, with the result that the material is repeatedly exposed to the physical and chemical agents of weathering. One of the most important organism in this regard is earthworm. These are - important in many ways. The amount of soil that these creatures pass through their bodies annually may amount to as much as 15 tons of dry earth per acre. a startling figure! During the passage through the worms, not only the organic matter which serves the earthworm as food, but also the mineral constituents are subjected to digestive enzymes and to a grinding action within the animal. There is usually an abundant growth of grass around earthworm casts. this suggests an increased availability of plant nutrients therein. Thus the activity of earthworm not only mixes the soil, but also makes it fertile by increasing its aeration and drainage. They also bring the lower soil to the surface. They mix and granulate the soil by dragging into their burrows, large quantities of undecomposed organic matter such as leaves and grass. which they use as food.Burrowing animals dso bring great quantities of subsoil to the surface. In addition, these animals cut and bury the litter of which some is used for food ahd some as nesting material. The latter, together with their excreta buried below the surface, greatly increase the organic content which contribute to soil fertility.