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Earthworms have a beneficial effect on the physical and chemical properties of soil. Earthworms change the structure of the soil and improve its ability to cycle nutrients. The burrowing of earthworms aerates the soil and improves water drainage. As earthworms dig through compacted soil, they ingest the soil and grind it up. They move organic matter from the surface and mix it deeper into the soil. In the forest, this organic matter is called duff, mostly litter from fallen leaves and decaying branches.
Earthworms benefit plants in every conceivable way. Their burrowing creates channels through which plant roots may more easily penetrate the soil. Earthworms aid in the formation of humus, the organic matter in soil. A high level of humus is associated with soil fertility, so worms are beneficial to forests, agriculture, and gardens. Worm excretions are a valuable source of nitrogen, which assists in plant growth. The bodies of earthworms are rich in proteins, minerals and vitamins, and when worms die these nutrients are released into the soil.
Earthworms are an important link in the food web because they are a food source for numerous species of animals. They are preyed upon by many species of birds, snakes, and mammals, as well as invertebrates such as beetles and snails. Earthworms are also used as bait in sports fishing and as animal feed in poultry farming. With the help of gardeners and sports fishermen, earthworm populations continued to spread, sometimes at the speed of ten meters a year. Wherever they go, earthworms are a positive force in the ecosystem.
Summarize the points made in the lecture, being sure to explain how they refute specific points made in the reading passage.