Have you ever shoveled soil in your backyard and dug up a bunch of worms? Worms have a symbiotic relationship with soil, meaning that the soil and the worms benefit each other. Soil provides protection, habitat, and nutrients for the worms. On the other hand, worms help the soil by digging their way up and down the soil layers. This movement does two things.
First, the worms create channels that allow water and air to pass through easily. Both of these things are important to soil structure and the channels make them more available for plants to absorbs through their roots. Speaking of roots, these channels also create an easy place for roots to grow. Secondly, when worms move up and down in the soil they are essentially stirring things up. The worms go up to the surface and pull down decaying matter that then breaks down in the soil layers breaking down nutrients for uptake by plant roots. It is like baking a cake! You can’t just dump all the ingredients in a bowl and expect it to bake well; you have to stir it first.