As earthworms crawl through tightly packed soil, they break it apart, making it more porous. Why would this be good for plants?
Consider the tunnel system earthworms could create in tightly packed soil. This allows for two benefits: aeration and drainage. Not only are they digging the channels for air and water to move through, but they are also acting as live "pumps" (if you will) of that air and water, as they move through their own tunnels.
Earth worm is called the friend of the farmer and plants. Because their part is great in the ecofriendly space. The earthworm converts the organic matters like dead plant parts, leaves etc into humus. The humus is extremely plant nutrient.The earth worm plows and burrows the earth creating its tunnels. This helps air circulation and conserve the water content of the soil. The action helps plant spread the roots farther and deeper in the soil besides having easy acces to their nutrient resource in the soil.The earth worms are even capable of ingesting rough soil particles and even small stones (1.25 mm wide) and it is digested and cast out as excreta of smooth paste. Their excreta is also rich with mineral , nitrogen , phosphate and potash contents that are a required by plants.